MEXICO CITY — Hundreds of striking teachers blocked the main road to the Mexico City international airport for the third time in two months on Tuesday, in a new protest against education reform.

Hundreds of police officers lined up to prevent the protesters from advancing on the boulevard. Metro stations near the airport shut down.

Twice  in recent weeks, teachers have disrupted traffic near the airport, as they protest a new law requiring them to undergo performance evaluations.

Airport director Alfonso Sarabia told Televisa television that flights have not been impacted so far and that the airlines would allow travelers to check-in as late as 15 minutes before a flight.

Ruben Nunez, a leader of the dissident CNTE union, said the teachers wanted a meeting with the federal government.

Thousands of teachers, mainly from southern impoverished states, have held protests in the capital for almost two months to demand that the government withdraw or modify the reform championed by President Enrique Pena Nieto.

The educators, who argue that the law violates their labor rights, had occupied the city's historic Zocalo square for weeks until riot police removed them on September 13.