MEXICO CITY — Mexico’s Catholic bishops called for an overhaul of the country’s education system, saying in a pastoral letter that the powerful national teachers’ union and its leader put politics and other issues ahead of teaching children.

The letter, written by Bishop Alfonso Cortes of Cuernavaca and released Sept. 12, said the practices of the 1.4 million-member National Education Workers Union — Latin America’s largest labor organization — led to corruption and the misuse of resources. The letter said the union’s actions were “seriously contaminating the task of educating.”

The letter comes at a controversial time, in which the union — an institution with anti-clerical tradition and self-proclaimed champion of the secular state — has come under attack for its role in the Mexican political system and willingness to put teachers on the public payroll to work for noneducational purposes.

And it touches on topics plaguing present-day Mexico, including the fact that millions of youths are unable to study or work and thus are vulnerable to recruitment by drug cartels. The document questioned the quality of what was being taught in Mexico’s schools, especially for not imparting critical thinking skills.

“It’s necessary to teach … how to think, to be critical and not just comply with predetermined objectives,” the letter said. It criticized teachers for not “discovering (students) authentic dignity and their service vocation in society.”

The letter’s publication comes as the church has called for the introduction of religious curriculum in a school system constitutionally mandated to be secular. The topic of religion in education is controversial as church leaders have objected to nationally distributed textbooks, which include portrayals of church leaders as opponents of Mexico’s independence and revolution.

Bishops’ conference president Archbishop Carlos Aguiar Retes of Tlalnepantla said church leadership wants religion taught in general with no special status assigned to Catholicism, which 84 percent of Mexicans profess.

The archbishop downplayed the document’s criticism of the union at a news conference announcing its release.

“In the document, we try to build bridges,” he said. “We’re not here to judge the persons or judge the structures (of the union), rather to say what’s lacking, that how we can help.”

Church help may not be welcomed by the union or by teachers, whose role in the post-revolutionary period early in the 20th century was to counter the influence of priests through public education.

Many teachers were targeted by Catholics fighting in the Cristero Rebellion of the 1920s for incorporating anti-clerical concepts promoted by the then-President Plutarco Elias Calles in the classroom.

The Institutional Revolutionary Party, which Elias Calles founded, ruled Mexico for much of the 20th century under a corporatist system in which teachers — through its national union — would mobilize voters, gain sway in the Public Education Secretariat and impart revolutionary values including secularism. Parents were to stay on the sidelines.

“There was a great fear about the Catholic heritage of the parents,” said David Calderon, director of the education advocacy group Mexicanos Primero. “Parents were left outside of the school, of decisions, and generation after generation had an obligation as parents to leave their children in the school and hope that by having more years of schooling they would have better earnings.”

Mexicanos Primero has been critical of the union and its longtime leader Elba Esther Gordillo, perhaps the most powerful woman in Mexican politics. The organization describes the Mexican education and union situation in a documentary titled, “De Panzazo!” The title is a slang term meaning scraping by, which the organization alleges is common in Mexican schools.

The film cited statistics from international standardized exams showing Mexican students achieving among the lowest scores in math and science in the developed world. Teachers, meanwhile, were taken to task for their frequent protests and work stoppages.

“The privileges derived from the centralization and from corporatist and patronage practices generated a structure of domination and control that have jeopardized the education process,” the pastoral letter said.

On Gordillo’s leadership, the document said indirectly, “It’s the duty of everyone to work together so that the unions are not co-opted by eternal leaders or ideologies foreign to education.”

The national union has rejected allegations that it is ignoring its duties and is running ads to bolster its image. Gordillo has questioned the attacks against her, but has made no secret of her political power, especially boasting of backing President Felipe Calderon’s 2006 campaign in exchange for putting her people, including her son-in-law, in three senior positions.

Calderon subsequently won a close election, a reflection of the teachers’ ability to get out the vote and their lingering ability to wield influence — along with priests and physicians — in remote regions.

Political historian Ilan Semo of the Jesuit-run Iberoamerican University expects the incoming government, which takes office Dec. 1, to continue making concessions to the union in exchange for political support.