Just as with peah (the corner of the field), leket – the gleanings – has both a positive and a negative aspect. As stated in the previous mitzvah, we commanded to leave one or two dropped ears of grain for the poor. This mitzvah prohibits us from picking them up.
This prohibition applies to both men and women but only in Israel. It is discussed in the fourth chapter of tractate Peah in the Mishnah and is codified in the Shulchan Aruch in Yoreh De’ah 332. It is #211 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #7 of the 26 mitzvos that can only be performed in Israel according to the Steipler Gaon.