Gil Fowler and Mike Tenorio (petitioners) contend that the San Francisco Web Pressmen and Platemakers’ Union No. 4 (the Union) breached its duty of fair representation in violation of National Labor Relations Act (NLRA) § 8(b)(1)(A), 29 U.S.C. § 158 (b)(1)(A) by making no effort to obtain their version of the events that led to their discharge before processing their *600 grievance. The National Labor Relations Board found in favor of the Union. We reverse.

FACTS

Petitioners joined the Union upon commencing employment with the San Francisco Newspaper Printing Company (employer) in November, 1977. 1 In August, 1978, petitioners became involved in a barroom altercation with a fellow Union member. Although the fight occurred away from the employer’s premises, the Union initiated an investigation. Upon learning of the petitioners’ involvement in the fight, the Union Executive Board asked Fowler and Tenorio to appear before it to answer questions. They decided not to appear, thinking that the fight had been a private matter of no concern to the Union. They telephoned Paul Trimble, an Executive Board member to inform him of their decision. Uncertain that Trimble had understood their position, petitioners visited Trimble at work.

Trimble reported the pressroom confrontation with petitioners to his foreman and claimed to have felt threatened. 2 The foreman related Trimble’s story to other supervisors, who decided to discharge the petitioners. The employer formally discharged petitioners early the next day.

Upon learning of the discharge, Union President Richard Munger filed a grievance on the petitioners’ behalf. At the direction of Vice-President David Ratto, the Union also immediately prepared travel cards 3 for petitioners, effectively barring them from working as pressmen in Northern California.

The Union conducted an investigation of the confrontation between Trimble and the petitioners. Munger interviewed Trimble and two eyewitnesses. However, despite its policy of talking to discharged workers to get their story regarding discharges, the Union never interviewed Fowler or Tenorio, purportedly because it had neither their addresses nor telephone numbers. Yet, one Union official testified that he had had addresses for both men at the time of the investigation. Moreover, Ratto met twice with petitioners prior to the first stage of the grievance proceedings, a meeting of the Joint Standing Committee, without making inquiry into petitioners’ explanation of the pressroom conversation.

The Joint Standing Committee, composed of two employer representatives and Mun-ger and Ratto, met and reviewed the merits of the grievance. Among the evidence considered were written statements made by Trimble and the two eyewitnesses. No effort was made to contact or confer with either Fowler or Tenorio. Munger and Rat-to decided, based on the written statements and “on the entire circumstances and merits of the whole grievance,” to acquiesce in the dismissal; the Union decided “not to pursue it [the grievance] to arbitration”. The Union’s membership subsequently voted to approve the Union’s settlement of the grievance.

Petitioners then filed a claim with the National Labor Relations Board. An administrative law judge (ALJ) concluded that, although the Union had harbored no animosity toward petitioners, it had processed their grievance arbitrarily and perfunctorily. He reasoned that because Fowl *601 er’s remarks to Trimble were susceptible to more than one interpretation, the Union was obligated at least to attempt to obtain petitioners’ explanation of their conduct. The Union’s failure to make such an effort constituted a breach of its duty of fair representation. The Union appealed that decision to the Board, which reversed, finding that under the circumstances of this case, the Union had no duty to attempt to learn petitioners’ story. Petitioners appeal from the Board’s decision. We have jurisdiction pursuant to NLRA § 10(f), 29 U.S.C. § 160 (f).

DISCUSSION

A. The Standard of Review

We cannot review the Union’s conduct de novo. Instead, we accept as conclusive the Board’s findings if substantial evidence in the record as a whole supports those findings. 29 U.S.C. § 160 (f); Universal Camera Corp. v. NLRB, 340 U.S. 474, 488 , 71 S.Ct. 456, 464 , 95 L.Ed. 456 (1951); NLRB v. Big Bear Supermarkets No. 3, 640 F.2d 924 , 928 (9th Cir.), cert. denied, 449 U.S. 919 , 101 S.Ct. 318 , 66 L.Ed.2d 147 (1980). The fact that the Board’s conclusion differed from that of the ALJ does not alter the applicable standard of review. NLRB v. Warren L. Rose Castings, Inc., 587 F.2d 1005, 1008 (9th Cir. 1978), but it causes us to engage in a “more searching” review. Doug Hartley, Inc. v. NLRB, 669 F.2d 579 (9th Cir. 1982). The ALJ’s decision is an integral part of the record and must be considered. Universal Camera Corp., 340 U.S. at 493 , 71 S.Ct. at 467 . Our task in applying the substantial evidence test is not merely to look for evidence supporting the Board’s finding, but to determine whether that evidence is substantial after taking into account whatever in the record fairly detracts from its weight. Universal Camera Corp., 340 U.S. at 488 , 71 S.Ct. at 464 ; NLRB v. Torneo Communications, Inc., 567 F.2d 871, 877 (9th Cir. 1978). We shall affirm the Board’s decision unless we can conscientiously find that its decision is not supported by substantial evidence. Dalewood Rehabilitation Hospital, Inc. vi NLRB, 566 F.2d 77, 80 (9th Cir. 1977).

B. The Duty of Fair Representation

A union breaches its duty of fair representation if it processes a member’s grievance in an arbitrary or perfunctory .manner. 4 Vaca v. Sipes, 386 U.S. at 190-91, 87 S.Ct. at 916-917. To comply with its duty, a union must conduct some minimal investigation of grievances brought to its attention. NLRB v. American Postal Workers Union, 618 F.2d 1249, 1255 (8th Cir. 1980); De Arroyo v. Sindicato De Trabajadores Packinghouse, AFL-CIO, 425 F.2d 281, 284-85 (1st Cir.), cert. denied, 400 U.S. 877 , 91 S.Ct. 117 , 27 L.Ed.2d 114 (1970). The thoroughness with which unions must investigate grievances in order to satisfy their duty varies with the circumstances of each case. Although we afford unions a reasonable range of discretion in deciding how best to handle grievances, union conduct that shows an egregious disregard for the rights of union members constitutes a breach of the duty of fair representation. Ness v. Safeway Stores, Inc., 598 F.2d 558, 560 (9th Cir. 1979) (per curiam); Robesky v. Qantas Empire Airways Ltd., 573 F.2d 1082, 1086 (9th Cir. 1978).

Petitioners contend that the Union’s investigation was so grossly inadequate as to transcend negligence and poor judgment. They argue that, by making no effort to hear their explanation of the events that resulted in their discharge, the Union showed a reckless disregard for their rights and thereby breached its duty of fair representation. We agree.

*602 The circumstances of this case indicate that the Union handled petitioners’ grievance arbitrarily and perfunctorily. First, the record indicates that the Union departed from its policy of interviewing all discharged employees to obtain their story before processing their grievances. Because unions must adhere to rational decision-making processes, NLRB v. General Truck Drivers, 545 F.2d 1173 , 1175 (9th Cir. 1976), the Union’s departure from its policy causes us to inquire whether the Union had a legitimate basis for doing so. We find none. The Union had ample opportunity to ascertain petitioners’ version of the press-room conversation that led to their discharge.

Second, the dispute in this case involved a Union official — Trimble—and therefore involved potential conflicts of interest for the Union in its handling of the grievance. In its role as the employees’ exclusive representative, the Union must be careful to protect the interest of all those whom it represents. Vaca v. Sipes, 386 U.S. at 177, 87 S.Ct. at 909: Ford Motor Co. v. Huffman, 345 U.S. 330, 337-38 , 73 S.Ct. 681, 685-686 , 97 L.Ed. 1048 (1953). Union officials must be cautious not to succumb to the influence of personal preferences. American Postal Workers Union, 618 F.2d at 1255 . Disputes involving both a union official and a union member may give rise to a tension between the union’s loyalty to its officials and its duty to rank-and-file members. We think that this possible conflict of interest places an additional responsibility on the union to assure that it handles its members’ grievances fairly. The Union should have made at least some effort to learn petitioners’ version of the pressroom confrontation.

Third, the fact that the Union promptly issued travel cards to petitioners suggests that it intended to handle their grievance in a summary manner. This action showed that the Union had accepted Trimble’s version of what had happened without even attempting to hear petitioners’ story.

Finally, the Union needed to exercise special care in handling petitioners’ grievance because they concerned discharges, the most serious sanction an employer can impose. See Griffin v. International Union, 469 F.2d 181, 183 (4th Cir. 1972). We find no indication in the record that the Union took special care with petitioners’ grievance.

In light of these considerations, we cannot conscientiously find that substantial evidence supports the Board’s finding that the Union was not obligated to attempt to ascertain the petitioners’ version of the events that led to their discharge. The totality of these circumstances indicates that the Union’s handling of petitioners’ grievance was so inadequate and showed such an egregious disregard for their rights that it constituted a breach of the duty of fair representation. In reaching this conclusion, we are not second-guessing the Union’s assessment of the merits of petitioners’ grievance. 5 We recognize that a union’s responsibilities often require it to assess the relative merit of the grievances presented by its members. See Vaca v. Sipes, 386 U.S. at 191, 87 S.Ct. at 917; Fountain v. Safeway Stores, Inc., 555 F.2d 753, 756-57 (9th Cir. 1977). However, the duty of fair representation requires that, before assessing the merits of a grievance, a union must have an ample basis upon which to make such an assessment. The Union in the instant case lacked such a basis.

Both the Board ’and the employer, an intervenor in this action, warn that ruling in favor of petitioners will effectively establish a per se rule requiring unions to *603 obtain explanations from every grievant or discharged employee. These warnings overstate the reach of our holding. We have based our conclusion on the particular circumstances of this case.

REVERSED and REMANDED to the Board for further proceedings in accordance with this opinion.

. Both men had previously worked in the Washington, D.C., area, which they left after losing their jobs because of violent strike activities.

. Upon finding Trimble in the pressroom, Fowler addressed him in a loud voice, asking to speak with him. When Trimble invited Fowler to talk he declined, replying “I don’t want to talk to you here. Let’s go out — Let’s walk outside. I want to talk to you outside.” Trim-ble refused to leave the pressroom. Fowler then asked Trimble when he got off work. Upon receiving Trimble’s response, Fowler remarked, “I’ll talk to you then.” During this exchange, Tenorio remained quiet. Neither Fowler nor Tenorio met with Trimble after he left work at 5 a. m.

. Travel cards are usually issued at the request of an employee who plans to leave the area. They indicate that the holder is a member of the union in good standing, having paid all dues and not having any outstanding fines. The cards, however, preclude the holder from further dispatch by the issuing union chapter.

. Although discriminatory or bad faith dealings by a union with any of its members constitutes a breach of its duty of fair representation, Vaca v. Sipes, 386 U.S. 171, 190 , 87 S.Ct. 903, 916 , 17 L.Ed.2d 842 (1967), we need not decide whether the Union in the instant, case harbored animosity toward petitioners or handled their griev-anee in bad faith. The ALJ found no animosity, discrimination, or bad faith. Because neither party excepted to this finding, the Board accepted it as true, and we must do the same. Detroit Edison Co. v. NLRB, 440 U.S. 301 , 311-12 n.10, 99 S.Ct. 1123 , 1129-1130 n.10, 59 L.Ed.2d 333 (1979).

. We are neither asked to, nor do we, intimate any opinion regarding how the merits of petitioners’ grievance should be decided. We note, however, that the dissent states that it is extremely doubtful that Tenorio and Fowler’s version of the incident would have been given any weight by the employer or have altered the Union’s conclusion that the grievance was mer-itless. Accordingly, Judge Hug concludes that if there was any error, it was harmless. Whether the employer would have been influenced is not the question. The interviews could have resulted in the Union deciding to submit the case to arbitration. Where, as here, the incident is subject to varying inferences depending on perceptions and tones of voice, it is entirely possible that a different result could have ensued.