Proposed cuts to English language classes for immigrants contradict the government's own policies on integration, MPs have warned.
£279m was spent on teaching English in 2004/05
Almost 100 MPs have signed a motion complaining about proposals changing who is eligible for the free classes.
Conservative MP Boris Johnson said immigrants were "baffled" by the measures coming into force this year.
Education minister Bill Rammell described the current funding set-up as "unsustainable" as demand has tripled.
Between 2004-05, the government spent £279m funding almost 540,000 places on English for Speakers of Other Languages courses (Esol).
These courses have long been considered a key element in helping either newly arrived migrants, or those already settled in the UK, to gain sufficient knowledge of the language to integrate more fully into society.
But under current proposals, Esol classes will no longer be free except for priority groups - the unemployed and those on income support. The changes are due to come into force in the next academic year.
The Department for Education says DFES funding will remain comparable but will be better targeted at those who most need it while working migrants will be expected to pay.
Campaigners say two key groups will be most affected - migrants in minimum wage low-skills jobs and some categories of asylum seekers or refugees.
Last autumn a think-tank study of Esol said demand was high and growing.
Researchers at the National Institute of Adult Continuing Education said it had serious concerns over the quality and scale of Esol teaching.
It also urged the government to force employers to provide English classes if they bring in overseas labour.
An understanding of English is now a key element of citizenship tests and in October 2006, Prime Minister Tony Blair underlined the importance of language to community cohesion.
Separately, communities secretary Ruth Kelly said she would launch a review of language services after BBC figures suggested public bodies were spending at least £100m on translation and interpretation services for UK residents.
At Education questions in the House of Commons, Labour's John Grogan told MPs that the cuts appeared to run contrary to policy.
"Cuts in funding for training in English for speakers of other languages, effectively ending free tuition for low-paid migrant workers from next September, is rather at odds with statements from ministers about the central importance of migrant workers learning English," he said.
For the Conservatives, Boris Johnson said the cut had left migrants "baffled" at the logic. On the government's own figures, nearly half of those currently receiving free classes would no longer do so because of the retargeting.
But Higher Education Minister Bill Rammell said there needed to be a "level playing field" between people who came to the country and British citizens.
"I do think it is important that migrant workers learn English. Both the numbers and the funding has tripled in recent years. But the current funding framework is unsustainable."
Mr Rammell said the government wanted to see both individuals and employers paying for Esol classes.