Yerushalmi Bava Metzia 6:2 ירושלמי בבא מציעא ו׳:ב׳

MISHNAH: If somebody hired tradesmen¹Independent contractors. and they backed out they are disadvantaged²⁵The contractor can only claim the difference between the contract sum and what was paid to his substitute..; if the householder backs out, he is disadvantaged²⁶He has to pay the contractor’s claims in full.. Anyone changing the terms of a contract is disadvantaged²⁷Mishnah Bava Qamma 9:5.; anyone backing out of a contract is disadvantaged.

HALAKHAH: “If somebody hired tradesmen,” etc. Rav said, “because the Children of Israel are My servants²⁸Lev. 25:55.,” Jews cannot buy one another. Rebbi Joḥanan said, this was stated about a Hebrew slave²⁹The verse is in the paragraph about a Hebrew slave of a Gentile, who has to be freed in the Jubilee year.. In Rav’s opinion, both a worker and an employer can back out; in Rebbi Joḥanan’s opinion the worker can back out but not the employer³⁰It seems that the attributions have to be switched. Rav, who quotes the verse, holds that a contract which bars a worker from quitting his job is invalid as “stipulating against the words of the Torah”, must hold that any employment contract which specifies a fixed term of employment can be enforced only against the employer, not the employee. In the Babli 10a this is universally accepted. This does not exclude that the worker who quits his job in the middle of work be financially disadvantaged (Babli 77a). R. Joḥanan, who holds that the verse is irrelevant in the context, must read the Mishnaiot as applying both to contractors and workers; both can renege on their obligations if they accept the penalties spelled out there..