Thousands of teachers demonstrated in Mexico City and some scuffled with police keeping them away from President Enrique Pena Nieto's residence, one day after he signed a controversial education reform.
Anti-riot police fortified the area around the Los Pinos residence with metal barriers and trucks to keep protesters at bay, with police saying some 12,000 teachers caused huge traffic jams as they marched across the megalopolis.
Some 80 officers used their shields to block advancing protesters, raising tensions with both sides pushing one another and coming to blows.
A delegation from a dissident teachers' union was allowed to go into the resident but came out disappointed after they were received by low-level officials.
Striking teachers have camped out in the central Zocalo square for the past three weeks and held several protests that have angered residents frustrated by the extra traffic jams they have caused in the already congested city.
But the teachers failed to stop Congress from passing Pena Nieto's reform, which he signed into law on Tuesday.
Smaller protests were held in several other states with thousands of teachers blocking a highway connecting Mexico City to the Pacific resort of Acapulco for several hours in the state of Guerrero.
Their anger is directed at a reform that strips the power of unions over education and requires teachers to undergo mandatory performance evaluations to get jobs and promotions.
The teachers, however, argue that the national test fails to take into account the fact that many work in rural and mountain classrooms in indigenous villages where standards must adapt to children who learn native languages before Spanish.
Juan Garcia, a leader of the National Education Workers Coordinator (CNTE) union, said the teachers want "the population to join the struggle" against the reform.
The union has not indicated whether it would vacate the Zocalo before Mexico's independence day celebration this weekend. City authorities have refrained from using force to remove the teachers.
The president traditionally delivers the "Cry of Independence" on the night of September 15 from the balcony of the National Palace, facing the Zocalo. A military parade is held at the square the next day.
Garcia said that "the next hours will be decisive to determine the action (the teachers take) on September 16."
Interior Minister Miguel Angel Osorio Chong insisted Tuesday that the independence celebration will take place at the Zocalo.