Police in Mexico City clashed with protesters during an operation to clear a square occupied by striking teachers.
Riot police, backed up by tanks and helicopters, broke through the barricades set up by the teachers shortly after a deadline for them to disperse passed on Friday. Some demonstrators responded with petrol bombs.
The BBC reports that teacher unions are against education reforms approved by President Enrique Pena Nieto. The changes include mandatory performance-related tests for teachers.
Police said they wanted to clear Zocalo Square for Independence Day celebrations this weekend.
Most of the protesters left peacefully by Friday's deadline. The BBC reports water cannons and tear gas were used against protesters throwing missiles in the square and the streets nearby.
Critics accuse teacher unions in Mexico of being corrupt and having too much control over job allocation.
Last week, their members protested outside the Senate in an attempt to disrupt the passing of the bill, which had already been approved by the Chamber of Deputies.