The National Teachers Union said 52,000 teachers were barred from entering schools, affecting some 875,000 pupils. Thousands of teachers held impromptu protests throughout Denmark, carrying signs and wearing white T-shirts expressing concern over a possible decline in the quality of education.

The showdown centers on who has the power to schedule teachers´ working time.The union has refused to accept a new working agreement that is part of sweeping school reform program.

Municipal authorities want the right to determine how much time teachers spend in the classroom, and reject the Teachers Union´s demand for a cap of 25 hours per week in class, with the rest of their working hours used for class preparation. Teachers currently spend on average 16 hours a week in the classroom.

If the two sides fail to reach an agreement, the central government could step in and force teachers back into schools.