Justice Kennedy writing for the majority, in language that is music to a defendant's ears, says it bluntly: "This, of course, is a lessened causation standard."
Looking beyond this victory, does today decision (coupled with Gross) establish a default standard for all federal employment law statutes? Maybe.
Justice Kennedy set out this rationale:
The approach respondent and the Government suggest is inappropriate in the context of a statute as precise,complex, and exhaustive as Title VII. As noted, the laws at issue in CBOCS, Jackson, and Gómez-Pérez were broad, general bars on discrimination. In interpreting them the Court concluded that by using capacious language Congress expressed the intent to bar retaliation in addition to status-based discrimination. See Gómez-Pérez, supra, at 486–488. In other words, when Congress’ treatment of the subject of prohibited discrimination was both broad andbrief, its omission of any specific discussion of retaliation was unremarkable.The last part was the Court's way of explaining its prior (in my view) overly broad expansion of retaliation where Congress had not specified it.
Going forward in reviewing other statutes, unless Congress specifically used "motivating factor" or other similar language, e.g. the language from SOX, "protected activity was a contributing factor in the unfavorable action," "but for" is the likely test.
My guess is that this will turn out to be a chronological issue. Certainly any statute before 1991 is unlikely to have such specific language, but probably most statutes passed after the Civil Rights Act of 1991 will.