Teachers have attacked politicians' meddling in the national curriculum and the censorship of English literature, warning against the schools secretary, Ed Balls, winning the power to dictate what pupils read and learn.

Delegates at the annual conference of the Association of Teachers and Lecturers (ATL) voted to raise the issue of censorship with Balls following the banning of Carol Ann Duffy's poem Education for Leisure, which refers to knife crime, from an AQA exam board anthology last year after "extreme pressure" from a group of MPs.

They are also opposing moves by Balls to gain new legal powers to dictate the basic content of public exams in England. They backed a motion calling for the ATL to "do everything in its power to prevent any government censoring texts and dictating what is studied in our schools".

Teresa Dawes, an ATL member from Park House school in Berkshire, said: "It rather makes one think of historical book burnings and all that implies. If young people don't get the opportunity to think critically about difficult but important topics in school, topics that often trouble them, where do they discuss them? The idea of any politician determining which parts of history or science children are taught or which books they study is indeed a chilling and frightening one," she said.

Ministers have defended the move to gain new powers over basic content of exams saying it would allow them to step in if exam boards were proposing to scrap Shakespeare, for example. The Department for Children, Schools and Families says the new law, part of the apprenticeships, skills, children and learning bill, will for the first time limit government interference by explicitly preventing politicians from intervening in matters of exam processes and standards.