462 U.S. 393 (1983)
Sam Santillo worked as a busdriver for Transportation Management Corp.1
On March 19, 1979, Santillo talked to officials of the Teamsters Union about organizing the drivers who worked with him.2 Over the next four days he discussed the possibility of joining the Teamsters with his fellow drivers and distributed authorization cards.3
On the night of March 23, 1979, supervisor George Patterson told one of the drivers that he had heard of Santillo's activities.4 Patterson referred to Santillo as two-faced and promised to get even with him.5 Later that evening Patterson talked to Ed West, who was also a busdriver for respondent.6 Patterson asked what was with Sam and the Union, said that he took Santillo's actions personally, recounted several favors he had done for Santillo, and added that he would remember Santillo's activities when Santillo again asked for a favor.7
On Monday, March 26, 1979, Santillo was discharged.8 Patterson told Santillo that he was being fired for leaving his keys in the bus and taking unauthorized breaks.9
Santillo filed a complaint with the Board alleging that he had been discharged because of his union activities, contrary to sections 8(a)(1) and 8(a)(3) of the NLRA.10 The Administrative Law Judge determined by a preponderance of the evidence that Patterson clearly had an antiunion animus and that Santillo's discharge was motivated by a desire to discourage union activities.11 The ALJ also found that the asserted reasons for the discharge could not withstand scrutiny.12
Patterson had not known about Santillo's practice until after he had decided to discharge Santillo, and the practice of leaving keys in buses was commonplace among respondent's employees.13 With respect to both coffeebreaks and stopping at home, the ALJ found that Santillo was never cautioned or admonished about such behavior, and the employer had not followed its customary practice of issuing three written warnings before discharging a driver.14
The Board affirmed, adopting with some clarification the ALJ's findings and conclusions.15 The Court of Appeals for the First Circuit refused to enforce the Board's order and remanded for consideration of whether the General Counsel had proved by a preponderance of the evidence that Santillo would not have been fired had it not been for his union activities.16 The Supreme Court granted certiorari because of conflicts on the issue among the Courts of Appeals.17
Whether the burden placed on the employer in Wright Line is consistent with sections 8(a)(1) and 8(a)(3) of the National Labor Relations Act as well as with section 10(c)?18
The General Counsel must prove by a preponderance of the evidence that protected union activity was a substantial or motivating factor in the discharge.19 Even if that showing is made, the employer may avoid liability by proving by a preponderance of the evidence that the discharge would have occurred for legitimate reasons regardless of the protected activity.20 This allocation treats the employer's showing as an affirmative defense and remains consistent with sections 8(a)(1), 8(a)(3), and 10(c).21
Yes. The General Counsel carried the initial burden through evidence of Patterson's statements expressing personal displeasure with Santillo's union activities and promising to remember them.22 The employer failed to prove that Santillo would have been discharged anyway, as the ALJ found the asserted reasons pretextual because the key-leaving practice was commonplace, breaks were tolerated, and customary warnings were not issued.23
The burden placed on the employer in Wright Line is consistent with sections 8(a)(1), 8(a)(3), and 10(c) of the NLRA.24