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Riot police moved into Mexico City's Zocalo Plaza on Friday to remove thousands of striking teachers from the historic square.

According to reports from CNN Mexico, El Universal and Milenio TV, the powerful teachers union, the National Coordinator of Education Workers or CNTE, was asked to remove its encampment, so the city could celebrate Mexican Independence Day on Sept. 16.

The CNTE refused and that's when a few hours ago, hundreds of police clad in riot gear surrounded the square.

Television images showed some protesters building barricades and starting fires. Helicopters flew over the square and bulldozers tore down the makeshift tents protesters had built.

NPR's Carrie Kahn tells our Newscast unit that protesters have been clashing with police on and off throughout the afternoon. She says that protesters taunt the police officers and throw garbage, rocks, and sticks at them. They respond by dousing them with pepper spray.

Last month, just as protesters set up the encampment, Carrie reported that teachers are "protesting education changes that would institute evaluations and reduce the power of unions in hiring educators." Carrie reported that the protesters had repeatedly closed down the main Reforma boulevard, "chased lawmakers out of Congress, and in the boldest and most disruptive move, shut down the thoroughfare to the airport, forcing tourists and travelers to walk to terminals under police escort."

The Los Angeles Times previewed a potential eviction, yesterday. As is tradition, President Enrique Peña Nieto is scheduled to deliver a Cry of Independence from the balcony of the National Palace.

But the protest puts a huge question mark over the tradition, so the government has been negotiating and said they were confident the square would be clear in time for the major celebration. The Times reports:

"This spring, CNTE members in the state of Guerrero took to the streets with pipes and brickbats, and on Wednesday in Mexico City, some pipe-wielding union members clashed with police in street demonstrations, leaving 17 officers injured.

"But if Peña Nieto had been forced to change his plans and issue his first Cry of Independence anywhere but the Zocalo, it probably would have been seen as an embarrassing sign of weakness. Critics were quick to mock Peña Nieto this month when the teachers sit-in forced him to move his first state of the nation address from the National Palace to Los Pinos, the official presidential residence a few miles away.

"Federal officials have been engaged in intense negotiations with the teachers. In public, they have maintained a confidential air. When asked Tuesday whether the cry would take place in the Zocalo, Interior Minister Miguel Angel Osorio Chong replied, 'Yes, of course.'"

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