dissenting:
Unlike the majority, I believe that substantial evidence supported the Board’s finding that the Union inconsistently enforced the hiring hall rules, and therefore that the Union was not entitled to use those rules as an affirmative defense against the charges of discrimination. Accordingly, I respectfully dissent.
For the most part, I agree with the majority’s statement of the law. As the majority explains, under the test established in Wright Line, 251 N.L.R.B. 1083 (1980), enforced, 662 F.2d 899 (1st Cir.1981), and approved by the Supreme Court in NLRB v. Transportation Management Corp., 462 U.S. 393, 401, 103 S.Ct. 2469, 76 L.Ed.2d 667 (1983), the NLRB’s General Counsel has the initial burden of proving by a preponderance of the evidence that retaliation for the union member’s protected conduct was “a substantial or a motivating factor” in the union’s action. Transp. Management, 462 U.S. at 400, 103 S.Ct. 2469; accord Office & Prof'l Employees Int’l Union v. NLRB, 981 F.2d 76, 85 (2d Cir.1992). Once that has been shown, the burden shifts to the union to prove, also by a preponderance of the evidence, that it would have taken the same action for valid reasons, even absent the improper motive. See Transp. Management, 462 U.S. at 400, 103 S.Ct. 2469; Office & Profl Employees Int’l Union, 981 F.2d at 85. To defend successfully on this basis, the Union must “establish that it acted pursuant to a concrete standard — be it a collectively bargained provision, a written union rule, or a long-standing practice,” Radio-Elecs. Officers Union v. NLRB, 16 F.3d 1280, 1285 (D.C.Cir.1994).
A union may not, however, rely on its hiring hall rules as a defense when the record shows that it inconsistently or selectively enforced those rules. See NLRB v. Laborers’ Int’l Union of North Am., 613 F.2d 203, 207-08 (9th Cir.1980). “When a union introduces an element, of discretion into what is otherwise a non-discretionary process, the union may be held accountable for discriminatory exercise [or enforcement] of that discretion.” Id. at 208. I also agree with the majority that substantial evidence supported the NLRB’s finding that the General Counsel established by a preponderance of the evidence that the Union’s refusal to refer James to the Northber-ry job was motivated by an unlawful desire to retaliate against James for filing an earlier complaint "with the NLRB. But I part ways with the majority on the issue of whether substantial evidence supports the Board’s conclusion that the union had not proven that it would have taken the same action absent the improper motive — i.e., I believe that substantial evidence supported the Board’s finding that, because the union had applied the hiring hall rules in an inconsistent and discretionary manner in the past, the union could not use those rules to prove its affirmative defense.
The standard by which we review decisions of the NLRB is highly deferential. This court must enforce the NLRB’s order if the Board’s “factual findings are supported by substantial evidence on the record as a whole.” NLRB v. Katz’s Delicatessen of Houston St., Inc., 80 F.3d 755, 763 (2d Cir.1996). This means that “reversal based upon a factual question will only be warranted if, after looking at the record as a whole, we are left with the impression that no rational trier of fact could reach the .conclusion drawn by the Board.” Id. at 763 (quoting NLRB v. Albany Steel, Inc., 17 F.3d 564, 568 (2d Cir.1994) (internal quotation marks omitted)). We must defer to the Board’s determinations on the credibility of the witnesses and on the weight to be given to different pieces of evidence. See, e.g., Abbey’s Transp. Servs., Inc. v. NLRB, 837 F.2d 575, 579 (2d Cir.1988)(“In reviewing the Board’s action in this regard, the test we apply is not whether we might make a different choice between inferences were the matter before us were the matter before us de novo, but whether there is substantial evidence on the record as a whole to support the Board’s finding.”).
*110The majority thoroughly — elegantly even — catalogs the substantial evidence that supported the Board’s finding that the Union enforced the hiring hall rules inconsistently. But it then improperly substitutes for the view of the Board its own judgment as to the weight to be given to that evidence.
The evidence included: (a) testimony that in the fall of 1994, four or five months after the Northberry incident, Ledwith skipped over Johnny Rodriguez’s name in violation of the hiring hall rules; (b) testimony that Led-with had violated the rules in January 1995 by referring James to a job even. though James had not signed the hiring hall sheet and had not been present in the hiring hall when the job was called; (c) evidence that Ledwith had the discretion to decide arbitrarily which workers received the longer duration jobs; (d) proof that, in May 1994, Ledwith referred minority workers to jobs when they were requested by name by employers, even though their names did not appear on the priority list, and despite the existence of other non-white workers on the priority list who had registered that morning at the hiring hall; (e) testimony that indicated that Ledwith, by utilizing “subjective determinations of skill levels” had breached the hiring hall rules by referring “three workmen who could not have been on the priority list .... ahead of workmen who may have and probably did possess the special bending machine skills”; (f) the fact that Ledwith had promised to refer James to the North-berry job, which suggested that Ledwith thought he had the discretion to make such a referral; (g) Ledwith’s testimony that it was his practice to select workers of equal priority based on an alphabetical sequence, rather than pursuant to the hiring hall rule that required referral according to which worker had registered earlier on the day in question; (h) evidence that Ledwith had referred Daryl Moore'to the Northberry job even though Moore had not signed the hiring hall sheet on the morning of referral.
The majority dismisses the bulk of this evidence by ruling that the NLRB was not allowed to consider rule deviations that occurred subsequent to the Northberry incident. The majority contends that “[e]vi-dence of hiring hall deviations occurring long after the action condemned is not relevant or probative to the issue of whether the Union failed to respect its referral rules at the time of that action.” Maj. Op. at 104.
But “[wjhen the state of an object at a particular time is in issue, we have repeatedly upheld the relevancy of evidence of that object’s condition before and after the time in question.” Lewis v. Baker, 526 F.2d 470, 474 (2d Cir.1975). We have further stated that “the weight to be given evidence of prior and subsequent condition differs in each case and is of course a question for the trier of fact.” Id. at 475; see also Manning v. New York Tel. Co., 388 F.2d 910, 912 (2d Cir.1968)(“Whether evidence of a subsequent condition should be admitted depends upon the time elapsed and the likelihood of a change in condition during that interval. Absent an abuse of discretion, a trial judge’s decision to admit such evidence will not be disturbed on appeal.”); Henry v. County of Shasta, 132 F.3d 512, 519 (9th Cir.1997), as amended, 137 F.3d 1372, 1372 (9th Cir.1998) (stating that “we reiterate our rule that post-event evidence is not only admissible for purposes of proving the existence of a municipal defendant’s policy or custom, but may be highly probative with respect to that inquiry” and collecting cases that support the view that the policies of an institution at a particular time can be demonstrated by evidence of subsequent events); School Bd. v. Department of Health, Educ. & Welfare, 525 F.2d 900, 908 (5th Cir.1976) (“In determining whether evidence of a subsequent condition may be utilized to establish its prior existence, we must consider both the time period which has elapsed, the nature of the fact to be established, and the likelihood of a change in that fact during the time interval.”) (citing 2 Wigmore, Evidence 437, at 413 (1940)); Facci v. General Elec. Co., 192 A.D.2d 991, 992, 596 N.Y.S.2d 928, 929 (App. Div., 3d Dep’t 1993) (“[Bjoth prior and subsequent accidents may be proffered to demonstrate that a product is dangerous or defective.”); DiLeo v. Lincoln Ctr. for the Performing Arts, 38 A.D.2d 830, 831, 329 N.Y.S.2d 637, 639 (App. Div., 2d Dep’t 1972) (“The admissibility of evidence of a prior or subsequent condition or existence of an object so as to *111give rise to an inference of such condition or existence at the time in question depends on the circumstances of the particular case.”); Missouri, Kan. & Tex. Ry. v. Williams, 103 Tex. 228, 125 S.W. 881, 882-83 (1910) (providing a classic statement of the evidentiary principle that “[w]hen the question is as to a condition existing at one time, evidence as to that at a different time” may or may not be probative, depending on whether the condition is “ephemeral” or “permanent or lasting”) (cited in Clark v. Commissioner, 143 F.3d 115, 119 n.1 (2d Cir.1998)).
The notion that prior or subsequent actions of an organization are relevant to prove the conduct of the organization on a particular occasion is acknowledged by Federal Rule of Evidence 406, which provides that “[e]vi-denee of the habit of a person or of the routine practice of an organization ... is relevant to prove that the conduct of the person or organization on a particular occasion was in conformity with the habit or routine practice.”
In the ease before us, the NLRB was entitled to consider the evidence of the Union’s subsequent violations of the hiring hall rules in determining whether the Union had a habit or routine practice of violating those rules. The evidence that Ledwith, during the relevant time frame, acted as if he had the authority to deviate from the rules, combined with the proof of his subsequent departures from the rules, was sufficient to support the Board’s finding. Ledwith, by promising to refer James to the Northberry job, acted as if he was willing to deviate from the rules at the relevant time. That same day, he referred Darryl Moore to the North-berry job, in clear violation of the rules and despite the fact that Moore had not signed the register. The majority inexplicably dismisses this event, which I emphasize once more occurred on the day of the retaliation, as “more akin to a simple oversight than evidence of union disregard for the referral rules.” Maj. Op. at 107. These facts, combined with the evidence of Ledwith’s deviations from the hiring hall rules on subsequent occasions, were, in my view, clearly sufficient to support the Board’s conclusion that the Union failed to prove that it would have taken the same action absent the improper motive.1
Were it our job to review the evidence de novo, I might agree with the majority. But in light of our duty merely to determine whether the NLRB’s factual findings were supported by substantial evidence, I cannot countenance the majority’s reweighing of the evidence. Accordingly, I respectfully dissent.
. I also disagree with the majority's stated reasons for dismissing some of the other evidence that showed that Ledwith had discretion in applying hiring hall rules. In particular, I am puzzled by the majority’s assertions that "discretion alone is not conduct that can vitiate a union’s affirmative defense under Wright Line," and that "[tjhere must be some showing that the Union wielded that discretion invidiously or arbitrarily.” Maj. Op. at 105. The nature of discretion is that it allows one to make arbitrary decisions, and thus permits discrimination by those who are of a mind to discriminate. See Laborers’ Int'l Union, 613 F.2d at 208 ("When a union introduces an element of discretion into what is otherwise a non-discretionary process, the union may be held accountable for discriminatory exercise [or enforcement] of that discretion.”). And in this respect, I once again note that the majority concedes the existence of substantial evidence supporting the NLRB’s finding that the Union's treatment of James was motivated by its unlawful desire to retaliate against him. But I believe it is not necessary to reach this question since the evidence of Ledwith’s actual deviations from the rules (as opposed to the evidence that he had considerable discretion under those rules) is sufficient to support the NLRB’s conclusion.