Bills to stop the sending of unwanted mail, which are modeled after the do-not-call phone registries, have been introduced in nearly a dozen states, raising fundamental legal questions about states’ ability to regulate the U.S. Postal Service.

In the last year, 11 states have introduced do-not-mail legislation calling for the imposition of hefty fines on marketers who mail solicitations to residents whose names are on do-not-mail lists.