At least a million children were left without classes in Mexico when a dissident teachers' group went on indefinite strike on this week, the Wall Street Journal reported.

Members of the National Coordinator of Educational Workers (CNTE), a branch of the national teachers union that is strong in the country's poorest states, also vandalized government offices, and torched electoral documents in what the newspaper called a "growing challenge to the administration of President Enrique Peña Nieto."

The teachers oppose mandatory evaluations the government had ordered in 2013 as part of an overhaul of the country's troubled public-school system, the newspaper explained. Officials said on Friday that those evaluation would be suspended "until further notice," a delay "broadly seen as a humiliating setback for the president."

Héctor Aguilar Camín, a prominent writer, used his Monday column in the Milenio newspaper to dub the move "the hardest blow the reformist credibility of President Peña Nieto has suffered so far," the Wall Street Journal said.

Meanwhile, the CNTE is insisting on the complete repeal of the president's education reforms and calling on Mexicans to boycott the legislative elections to be held on June 7, EFE noted.

In an interview with Radio Fórmula, the union's spokesman, Rubén Núñez, decried the vote, in which Mexicans are asked to select almost 2,000 public officials, including nine state governors and 500 federal lawmakers, as a "farce."

CNTE's demands "are not negotiable after the elections," Núñez warned. "The elections are a political circumstance, during with the National Coordinator of Educational Workers realizes boycott activities as part as our route (of action)."

In another high-profile stunt, union members on Wednesday shut down Xoxocotlán International Airport in the capital of the southern state of Oaxaca, EFE and the Associated Press reported.

The airport, which is served by United Airlines as well as domestic carriers, suspended flight operations after about 200 teacher occupied its facilities in what the newswires described as a non-violent protest. Otaki Toledo, the local CNTE spokesman, warned that the union could further "radicalize" its actions.