What is the limitation of an employer's right to invoke the statutory affirmative defense in cases that have yet to be filed?

same time, however, the legislature could have balanced this concern against a desire not to disturb the expectations of parties in ongoing litigation. Thus, it is certainly conceivable the legislature sought to impose a reasonable limit by allowing employers to invoke the statutory affirmative defense only in cases that had not yet been filed, or that were in the very early stages of litigation. In contrast, in cases that had been pending for a substantial amount of time prior to the statute taking effect, the legislature could have concluded the parties and the courts were more likely to have invested substantial resources and to have developed significant expectations. This approach is consistent with the idea that "the legislature must be allowed leeway to approach a perceived problem incrementally." Beach, 508 U.S. at 316. See also City of New Orleans v. Dukes, 427 U.S. 297, 303 (1976) ("Legislatures may implement their program step by step . . . in . . . economic areas, adopting regulations that only partially ameliorate a perceived evil and deferring complete elimination of the evil to future regulations.").