The grandfather clauses of many breed-specific ordinances are anything but true grandfathering. True grandfathering would mean that owners of specific breeds restricted by breed-specific legislation (BSL) who owned their dogs prior to the BSL being passed would be able to keep these specific breeds without any of the new restrictions being applied to them. However, passing an ordinance that requires pre-existing owners of banned or restricted breeds to adhere to new restrictions or to remove their dogs from the city or county entirely would be an ex post facto violation.
The ex post facto clauses are found within the U.S. Constitution, under Article 1, sections 9 and 10. Section 9 states:
No Bill of Attainder or ex post facto Law shall be passed.
Section 10 states:
No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility.
“An ex post facto law (from the Latin for “from something done afterward”) or retroactive law, is a law that retroactively changes the legal consequences of acts committed or the legal status of facts and relationships that existed prior to the enactment of the law.” Ex post facto violations occur when breed-specific legislation (BSL) is passed in a municipality or state and residents — who owned the banned or restricted breeds prior to them being banned are allowed to keep their dogs through what is erroneously called “grandfathering” — are still forced to comply with restrictions outlined within the BSL. Forcing prior owners of now banned or restricted breeds to comply with the new restrictions in exchange for them keeping their dogs is illegal per the ex post facto clauses and is not “grandfathering.” True “grandfathering” would be allowing prior owners of the banned or restricted breeds to remain unaffected; meaning, prior owners of banned or restricted breeds would not have to comply with the newly-passed law, whether a ban or restrictions, because they are “grandfathered” in.
For instance, say you live in a town that has just passed a breed ban against “pit bulls,” but which has allowed for prior owners to keep their “pit bulls” as long as they comply with guidelines found within the breed-specific legislation. The guidelines could be and often are mandatory spay/neuter or microchipping of the now banned “pit bulls” or a requirement to acquire a liability insurance policy on the “pit bulls” for some set amount. Applying these new restrictions to “pit bull” owners who owned their dogs before the legislation was passed would then be a violation of ex post facto law.
It should also be noted that ex post facto law is independent of property, equal protection, and due process law under the 14th amendment, of which breed-specific legislation is also in violation.