Detroit ? A judge on Friday ordered Detroit Public Schools teachers back to work after the district and the teachers union could not reach a tentative labor agreement despite nearly continuous negotiations.

Wayne County Circuit Judge Susan Borman said she had “hoped and was given hope” that the two sides could reach an agreement, but that the teacher’s 12-day-old strike threatened to irreparably harm Michigan’s largest school district.

Borman said the teachers must return to work by Monday. She also ordered the district and the 9,000-member Detroit Federation of Teachers to continue negotiating at least 12 hours per day through the weekend.