Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
65. It is a positive commandment for an owner of a house to give to his workers to eat from the crops that grow from the ground that they are working
As it is stated in Devarim (Deuteronomy) 23:25, "When you come into the vineyard of your friend, you can eat..." and it says in 23:26, "when you come into your friend's field of standing grain, you may pluck them..." According to our Sages, these verses are talking about a worker.
A worker may eat from the detached grains or from the grains that are still attached to the ground. This is as long as the attached grain's work has not been completed and this act completes the work [for the obligation of giving ma'aser or challah (tithes)]. This means, it cannot be before it is the completion of the work and not after the completion of the work, but only at the moment of the completion of the work. Because of the law of returning lost objects to owners [meaning lost time], our Sages have stated (in Bava Metzia 91b) that workers should eat while they are walking from place to place or when they are returning from the wine-press, in order that they do not waste time from their work by sitting to eat. They should eat during their work when they are walking and not be idle from work.
A person that guards standing crops is not allowed to eat at all because he does not do any actual labor. A person that guards detached grains, is not allowed to eat according to Torah law, but can eat according to the law of the land.
This applies in all places and at all times, for men and for women.