Sitting around a table in a dimly lit room, teachers and activists plot how to disrupt Sunday's midterm elections in an impoverished southern Mexico town fed up with corrupt politicians.

The town of Tlapa is home to some of the fiercest protests held by radical teachers who have vowed to block the elections for federal Congress, governor and mayors in the state of Guerrero in anger at the authorities.

But unlike their peers in Guerrero, neighboring Oaxaca and Chiapas, the main gripe of Tlapa's teachers is not President Enrique Pena Nieto's controversial education reform.

In this town surrounded by mountains where criminals grow opium poppies and marijuana, they are tired of elected officials who collude with drug gangs. Walls are covered with graffiti calling for a boycott.

"No to narco-elections," says a message spray-painted on a wall. Another says: "Don't cast a secret vote for someone who will rob you publicly."

"We want to block the elections because of the effects of the tyrannical relations between politicians and criminals. It would be giving power to the state to operate like criminals," said Elmer Pacheco, leader of the Popular Guerrerense Movement (MPG), a group formed by radical teachers.

- Burned ballots -

While the teachers refuse to reveal their plans for Sunday, protesters clashed with riot police on Friday, throwing rocks at the officers while a car burned in the middle of the road.

In the southern state of Chiapas, teachers broke into the regional offices of the country's main parties, took out furniture and documents that they burned outside.

Similar actions were taken this week against political parties in Oaxaca and Guerrero.

It was in the Guerrero city of Iguala last year that local police, under the orders of a crooked mayor, rounded up 43 college students and handed them over to a gang, which slaughtered them, according to prosecutors.

The Iguala case prompted teachers to seize the municipal government buildings of several Guerrero towns last year.

Tlapa was the only town where teachers still had control of government offices until Monday, when around 100 people, including local politicians, armed with bottles, sticks and stones forced them to leave.

- Imperial couple -

Before their ouster, the teachers had grabbed 80,000 election ballots from a house and torched them in the street, illuminating walls with graffiti demanding the safe return of the 43 students in several indigenous languages.

The MPG emerged in 2012 to reject Pena Nieto's education overhaul but the movement grew after the Iguala tragedy.

"First and foremost, we demand to see the 43. But at the same time (they want to block the elections) because we have allowed these people get to power," said Antonio Vivar, another teacher.

The teachers say they will take action overnight Saturday to deal a "hard blow" that could "destabilize the elections" in the town of 100,000 people, said Vivar, holding a book about Cuban revolution icon Ernesto "Che" Guevara.

Teachers call Tlapa's mayor, Victoriano Wences of the leftist Work Party, and his wife the "imperial couple." She's running for his seat while Wences is a candidate for Congress.

It is the same nickname that Mexican media gave to the mayor of Iguala, Jose Luis Abarca, and his wife Maria de los Angeles Pineda, who was also eyeing her husband's office and was accused of links with a drug gang.

Instead of elections, the teachers of Tlapa propose to create popular assemblies that would create government councils in every community, emulating indigenous customs.

They are inspired by similar systems in towns dominated by the EZLN Zapatista rebel movement in the southern state of Chiapas, and in Cheran, an indigenous town in the western state of Michoacan.

"Unfortunately this mountain region has the worst poverty numbers in the country while being one of the biggest producers of opium poppies," Pacheco said.

Tlapa is near Cochoapa El Grande, the poorest municipality in Mexico with 82 percent of the population living in extreme poverty.

"We are light years away from the image of the developed countries that the technocrats who govern us have," he said, fixing his glasses. "That's why we don't understand each other."