As many as 80,000 of Britain's poorest students could be priced out of taking even basic vocational qualifications if they are forced to pay their own fees, college leaders fear.
From next August, many people who rely on "inactive" benefits - such as income support, housing or council tax benefits and pension or working tax credits - will no longer be eligible for full fee remission for courses at FE colleges.
Among those who will lose out are over-24s taking level 3 qualifications such as NVQs, BTECs or OCR Nationals.
Others affected include students on basic courses below level 2 and those who have previously taken a level 2 or 3 qualification.
An advice note sent out by the Skills Funding Agency (SFA) said the measures had been designed by the Government to promote "fairness" by prioritising "those in need", targeting young adults, unemployed people on "active" benefits, including jobseekers' allowance, and employment support allowance, and people without basic literacy and numeracy skills.
But Julian Gravatt, assistant chief executive at the Association of Colleges, said the changes would cause "genuine hardship" for those who could least afford to pay their full fees and an estimated 70,000 to 80,000 adults could be deterred from staying in education.
He called for the scheme to be put back 12 months to allow the details to be fine-tuned. "The Government's work on getting people off benefits and refocusing the system will take a couple of years to put in place," he said. "It is premature to be taking remissions off before they have a new system in place."
Lewisham College principal Maxine Room has calculated that 18,000 people training at the 12 FE institutions that make up the London Capital College group, which she chairs, could lose out.
"In practice, they just won't enrol - it is totally unaffordable," she said. "We simply cannot believe that the Government meant to remove this vital support to help low-income households help themselves - it seems to run counter to the Government's principles of `fairness'.
"We want to be clear on the practical implications of this before huge damage is done to the supply of skilled labour and to the aspirations of thousands of adults."
South Thames College principal Sue Rimmer said the changes would exacerbate skills shortages at higher craft and technician level.
"This risks trapping people in some of the most disadvantaged communities on benefits dependency and will deny them opportunities to contribute to the country's economic recovery," she said.
Vicki Fagg, principal of the College of North West London, said students could have to fork out "substantial" fees of more than pound;2,000 even for a low-level construction course.
"The people who are impacted by this are the ones who can least afford it," she added. "FE offers a gateway of opportunity: the people who are studying for these skills are looking to do something about their dependency on benefits. This will undermine and inhibit colleges."
A spokesman for the Department for Business, Innovation and Skills said: "In tough economic times, it is right to prioritise funding for those most in need, including the unemployed and people who lack basic skills. It is fair that learners and employers should contribute towards the costs of intermediate and higher level training where they are able to."