In the article Lawsuit, Shmawsuit, Judge Alex Kozinski & Eugene Volokh argue that the influence of Yiddish has dramatically increased in legal slang since 1980. As for the word 'kosher', they write:
"But it’s clear that 'kosher' is used figuratively in quite a few cases, from United States v. Erwin’s insistence that the law 'tell the felon point blank that weapons are not kosher' to Texas Pig Stands, Inc. v. Hard Rock Cafe International, Inc., which concludes that 'though not entirely kosher, Hard Rock’s actions were not ... swinish.' Pig Stands is somewhat atypical, though, as its reference to 'kosher' is just one in a series of pork jokes."