Striking teachers seized 12 private radio stations in the southern Mexican city of Oaxaca and set buses on fire, as a long-running protest worsened
They acted after unidentified gunmen opened fire on a government radio station already under their control.
The strikers used the stations to tell parents to ignore Monday's start of the school year and keep children at home.
Teachers have been striking since May to demand higher wages and Oaxaca Governor Ulises Ruiz's resignation.
The shooting began at a government-owned radio station already in the hands of the striking teachers.
A number of rounds were fired by unknown gunmen, and the teachers say one of their members was injured.
The attack prompted a violent retaliation by the teachers, and a number of buses were overturned and set on fire.
Dozens of the protesters also took over the privately-run radio stations and started broadcasting messages of defiance.
Others armed with crude weapons blocked off some of the main roads into Oaxaca.
A spokesman for President Vicente Fox blamed the state government for attempting to take back the radio station by force.
He said the attack was carried out without consulting the federal authorities and described it as a unilateral decision by the governor of Oaxaca, Ulises Ruiz.
Mexico teachers grab Oaxaca radio stations, shot at
Teachers take over radio stations
Civil DisObedience In Mexico City, UnCivil DisObedience In Oaxaca