Opinion of the Court
990 (CADC 1977). While to the modern eye each of these examples may seem “plainly [to] constitut[e] discrimination because of biological sex,” post, at 38 (Alito, J., dissenting), all were hotly contested for years following Title VII’s enactment. And as with the discrimination we consider today, many federal judges long accepted interpretations of Title VII that excluded these situations. Cf. post, at 21–22 (Kavanaugh, J., dissenting) (highlighting that certain lower courts have rejected Title VII claims based on homosexuality and transgender status). Would the employers have us undo every one of these unexpected applications too?
The weighty implications of the employers’ argument from expectations also reveal why they cannot hide behind the no-elephants-in-mouseholes canon. That canon recognizes that Congress “does not alter the fundamental details of a regulatory scheme in vague terms or ancillary provisions.” Whitman v. American Trucking Assns., Inc., 531 U. S. 457, 468 (2001). But it has no relevance here. We can’t deny that today’s holding—that employers are prohibited from firing employees on the basis of homosexuality or transgender status—is an elephant. But where’s the mousehole? Title VII’s prohibition of sex discrimination in employment is a major piece of federal civil rights legislation. It is written in starkly broad terms. It has repeatedly produced unexpected applications, at least in the view of those on the receiving end of them. Congress’s key drafting choices—to focus on discrimination against individuals and not merely between groups and to hold employers liable whenever sex is a but-for cause of the plaintiff’s injuries—virtually guaranteed that unexpected applications would emerge over time. This elephant has never hidden in a mousehole; it has been standing before us all along.
With that, the employers are left to abandon their concern for expected applications and fall back to the last line
