City academies are targeting families from affluent areas and may not be providing a balanced curriculum, according to the National Union of Teachers.
In a pamphlet to be published later this month, Britain's biggest union cites six key reasons why parents and teachers should resist attempts to open academies in their areas.
Ministers want at least 53 academies by 2007 and a dozen have already opened. Usually the academies receive around pound;2 million from public or private sponsors and pound;8m from the Government.
In the pamphlet Academies: looking beyond the spin, the NUT claims that the academies:
* put schools in the hands of sponsors
* threaten fair admissions procedures
* threaten teachers' job security and conditions of service
* have a damaging effect on other local schools
* undermine the independent role of school governors
* threaten children's entitlement to a broad and balanced curriculum.
The NUT said that academies upset fair admissions in a variety of ways, including marketing themselves to families who live in leafier places outside their traditional catchment zone.
One school that had adopted this approach was the Bristol academy, which the union said had deliberately sent glossy leaflets to more affluent areas.
The NUT is also concerned by the influence that sponsors have over lessons.
Its pamphlet points to Professor Alec Reed, founder of the Reed recruitment firm, who has said he wants enterprise to be part of all aspects of the curriculum at the school he sponsors, the West London academy in Ealing.
"This begs the question of whether it is desirable for pupils to be drawn into the competitive world of work at the age of 11, or even earlier with the 'all-age' academies," the pamphlet states.
The NUT criticises the number of faith groups sponsoring schools, which it says raises questions about the academies' abilities to meet the needs of local multi-faith communities and adds to their selectivity.
This week the United Learning Trust, an arm of the Christian educational charity the Church Schools Company, revealed that it was the largest single sponsor of academies. It has raised more than pound;5m in two years to sponsor a network of six schools.
Ray Priest, head of the Bristol academy, denied his school was attempting to attract pupils from more prosperous areas. The school had placed leaflets in a free weekly newspaper which is distributed to homes across Bristol, he said, but it was already over-subscribed with local pupils.
Mr Priest added: "I think academies are a visionary approach to education in our cities and more children should benefit from them."
The Department for Education and Skills also defended the initiative. A spokeswoman said: "Academies are making a positive impact through the imaginative use of the freedoms and flexibilities available to them."