Tosefta על פאה 5:5

[If a poor worker] received [a one time job] to harvest a field, [then] his son cannot glean [the gifts to the poor right] after him [before other poor people will have a chance to glean that field]. Rebbi Yossi says, “His son may glean after him.” But sharecroppers, and [regular] tenants, and a person who sells his standing crops to his friend in order [that his friend should] harvest them, [in all of these cases] his (i.e. the sharecropper’s, or tenant’s, or friend’s) son can glean [the gifts to the poor right] after him [before other poor people will have a chance to glean that field]. If there were [in the field] poor people who are not fitting [to be allowed] to glean [the gifts to the poor, then] if the owner of the field can prevent them [from gleaning], he is allowed to do so, but if [he is] not [able to prevent them from gleaning, then] he should leave them alone [and let them glean anyway] because of peaceful relations [between people].