Mishnah, Bava Metzia 7:1
One who hires workers and instructs them to begin work early and to stay late—in a place in which it is not the custom to begin work early and to stay late, the employer may not force them to do so. In a place in which it is the custom to feed the workers, he must do so. In a place in which it is the custom to distribute sweets, he must do so. Everything goes according to the custom of the land [minhag hamakom].
A story about Rabbi Yochanan ben Matya, who told his son, “Go, hire us workers.” His son went and promised them food (without specifying what kind, or how much). When he returned, his father said to him, “My son! Even if you gave them a feast like that of King Solomon, you would not have fulfilled your obligation toward them, for they are the children of Abraham, Isaac and Jacob. However, as they have not yet begun to work, go back and say to them that their employment is conditional on their not demanding more than bread and vegetables.” Rabbi Shimon ben Gamliel said, “It is not necessary to make such a stipulation. Everything goes according to the custom of the place.”