Which preposition to use with unenforceable

in Occurrences 1%

The court declared the contract illegal (and hence unenforceable in a court) and administered a severe reproof to the craftsman who made it.

under Occurrences 1%

More recently the United States Supreme Court has held that a contract imposed upon a sailor whereby he agreed to ship as a mariner on the Pacific coast for a voyage to various other parts of the world and thence back was a contract so indefinite in length of time as to be unenforceable under free principles, although a sailor's contract is one which in a peculiar way carries with it indefinite service.

Which preposition to use with  unenforceable