Duke University students participating in a sit-in have rejected a proposed initiative by the university to raise the minimum wage for its workers and hire an outside expert to review employee grievance procedures.

News outlets report Duke President Richard Brodhead sent a letter to the campus community Wednesday, saying the university would take steps to improve school working conditions, including beginning to raise Duke's minimum wage to $12.

Within 30 minutes, protesting students said the concessions weren't enough. Among other demands, the students called for the school's minimum wage to be raised to $15 over the next several years.

Nine student protesters began a sit-in outside Brodhead's office Friday. The administrative building has been shut down for classes and visitors ever since. As of late Wednesday, eight students remained.