Wiktionary
black law
alt. (context US English) Any one of a series of laws, passed before the American Civil War, sharply discriminate against free negroes who wished to emigrate to a northern state and become citizens thereof. n. (context US English) Any one of a series of laws, passed before the American Civil War, sharply discriminate against free negroes who wished to emigrate to a northern state and become citizens thereof.
Usage examples of "black law".
Hay made of his old colleague's first name a sort of formal title, White Law, White Rod, Black Law, Black Rod, like those ancient ceremonial servitors of the British crown.