An ad hoc student group supporting the United Farm Workers called last night for a boycott on four House dining halls next week to protest non-union lettuce at Harvard.

The group will picket a different House dining room each night during dinner until next Friday. Monday morning the group will designate the first target of the boycott.

"We've chosen the boycott as a tactic so that the University won't fail to see, as it did in the case of the petition, that there is a significant mandate for action on this issue," said David P. Levin '71, a member of the student group.

Earlier this week, the group presented to the University food purchasers a petition signed by nearly 1700 students asking that Harvard buy only UFW lettuce. The purchasers informed the students that although 80 per cent of Harvard lettuce is union-picked, any decision to buy only union lettuce would violate both Harvard's neutrality and its economic obligation to the students.

The United Farm Workers Union has been negotiating a contract with the growers which increases wages to $210 an hour, provides medical insurance to workers after 50 hours in the fields, and bans the growers' use of DDT and other hard pesticides.