Legislatures sometimes address the risk that a court will declare all or part of a law unconstitutional by including "fallback" provisions that take effect on condition of such total or partial invalidation. The most common kind of fallback provision is a severability clause, which effectively creates a fallback of the original law minus its invalid provisions or applications. However, fallback law can and sometimes does take the express form of substitute provisions.
Fallback law can raise a surprisingly large number of constitutional and policy questions. A fallback provision itself must be constitutional, but how to discern the constitutionality of the fallback will not always be obvious, especially where the original provision's defect consists in its use of some impermissible procedure, for then courts will need to ascertain whether the fallback purges the taint of the original provision.
Fallback law can also be challenged as impermissibly delegating lawmaking authority, and one state, Oregon, forbids fallback law based on an express non-delegation provision of its state constitution. Although congressional use of fallback law does not violate federal principles of non-delegation, it can run afoul of the legislature's duty to consider the constitutionality of its enactments, regardless of whether that duty permits broad or narrow deference to the courts.
A legislature might adopt a fallback provision that does not aim to achieve the same basic objectives as the original provision, but instead penalizes the courts for invalidating it. By harming the courts or innocent third parties, a fallback can be used to coerce a ruling upholding the original provision. Such coercive fallbacks should be deemed unconstitutional, even on the assumption that the legislature could enact the same provision separately as an ex post response to an unpopular judicial decision.
Assuming legislators overcome the constitutional obstacles to fallback law, they face a policy tradeoff in deciding what event triggers the fallback. Awaiting a final ruling on the validity of the original provision by the U.S. Supreme Court or state high court means leaving in place a legal void, the very evil that fallbacks aim to prevent; yet, making lower courts' decisions trigger the fallback's applicability either creates legal inconsistency or gives those courts inordinate lawmaking power.
Accordingly, legislatures should always hesitate before crafting expressly substitutive fallback law and should sometimes hesitate before crafting severability rules.
Dorf, Michael C., "Fallback Law" (2007). Cornell Law Faculty Publications. Paper 78.
Columbia Law Review, vol. 107, no. 2 (March 2007)