Scores of England's colleges have already started axing jobs and courses as a result of funding cuts, according to a survey.
Public service union Unison and the University and College Union polled 247 colleges, and 146 replied.
Of those 93% said they had axed jobs, with 80% saying they had cut courses and resources.
The government said it was necessary to focus funding where its effect could be maximised.
The survey, conducted in the last few weeks, found support staff and teaching staff were taking the biggest hit.
'Cut to the quick'
Only 12% of colleges pointed to job cuts in management posts and 1% to senior posts being lost.
Union leaders raised concerns that funding has been "cut to the quick", with students pushed out of further education.
More than half (53%) of those questioned said other college posts were currently at risk.
Sixty colleges said they were planning to close courses over the next 12 months, while a further 42 said they were reviewing it.
Nearly one in four (23%) said they had been forced to turn potential students away because of cuts.
Chris Fabby, Unison's national officer for further education, said: "Colleges are being cut to the quick. They have already axed a huge number of jobs and courses. We fear for the future, as the survey shows that the worst is yet to come.
"Students are being forced out of further education altogether as the education maintenance allowance, fee remission and courses are slashed. These cuts are devastating learners, communities and local economies."
UCU general secretary Sally Hunt said: "In the week that Nick Clegg spoke about the importance of social mobility, this survey highlights the true cost of the government's cuts to education.
"Rather than helping to fund the very courses that people need to realise their potential, the government is slashing college budgets, putting teachers on the dole queue and removing vital lifelines such as the education maintenance allowance."
A spokesman for the Department for Business, Innovation and Skills said the government was committed to a strong further education system.
"In 2011-12, we plan to invest £3.9bn in FE skills for post-19 learners.
"In addition Budget 2011 included a £180m package for adult apprenticeships over the spending review.
"In the current economic climate it is necessary to focus investment where its impact is maximised."
It added that it would be increasing investment in apprenticeships, protecting investment in adult and community learning, basic literacy and numeracy courses for young adults.