CAMBRIDGE, Mass. (AP) — A union for Harvard University graduate students is staging a campus sit-in to pressure the school to meet its labor demands.

Roughly 20 students were gathered inside a building in Harvard Yard on Wednesday as others marched outside in support of the Harvard Graduate Students Union.

Harvard administrators and union representatives have been negotiating details of an initial labor contract for the group for about a year. The union says it’s pushing for higher wages, more affordable health care and stronger protections against sexual harassment. Harvard officials did not immediately provide comment.

Harvard graduate students voted last year to unionize with United Auto Workers. They join students at several other U.S. campuses that have organized since a federal panel ruled in 2016 that graduate student employees could form unions.