U.S. Constitution, Article I — The Legislative Branch, Section 2, Clause 4
When vacancies happen in the Representation from any State, the Executive Authority thereof shall issue Writs of Election to fill such Vacancies.
Notes
Requires the executive authority of a state to issue writs of election to fill any vacancy that happens in that state's representation in the House. The vacancy is filled by an election called by the state's executive, not by appointment, and the rule applies to every seat in the state's delegation.
Use as reference
Lexinter.net | U.S. Const. art. I, § 2, cl. 4 | https://laws.lexinter.net/constitution/us/article-1/section-2/clause-4