You shall not abuse a needy and destitute laborer, whether a fellow countryman or a stranger…You must pay him his wages on the same day…for he is needy and sets his life on it; else he will cry to God against you and you will incur guilt. (Deut. 24:14-15)
Keeping the salary of a worker is like taking his/her life, and transgresses five negative commandments and one positive command. Shulhan Arukh (Hoshen Mishpat 339:2)