Negative Mitzvah 267
It is forbidden for a hired worker to eat from the crops while working the field of his employer
Deuteronomy 23:26 "You shall not waive a sickle to your neighbor's standing grain"
Positive Mitzvah 201 allows a hired worker to eat from the fruit or grain that he is harvesting, but the worker must realize that he was hired to do a job.
This Negative Mitzvah forbids a worker who is hired to harvest from reaping crops for himself or eating when he is not allowed.
It also forbids a person hired to do other work besides harvesting from reaping grain for himself and eating while he is working for his employer.
Negative Mitzvah 268
It is forbidden to eat more than allowed when harvesting crops as a hired worker
Deuteronomy 23:25 "When you come into your neighbor's vineyard, then you may eat your fill of grapes at your desire; but you shall not put any in your container"
As mentioned, a hired worker may eat from the fruit or grain that he is harvesting. However, there are limits to how much he is allowed to eat.
It would be cruel to stop a worker from eating entirely, but this Negative Mitzvah forbids a worker from taking more than a fair share.
A hired worker in a vineyard may only eat enough grapes to satisfy his hunger. He is not allowed to gather grapes for himself and pack them away to take home or eat later.