Colleges stand to receive 10 per cent less in their teaching grant this year than last year, despite assurances from the education secretary that the cuts should be no more than 8.5 per cent.
Michael Russell wrote to FE college principals last week, saying he expected no college to see "a fall in teaching grant of more than 8.5 per cent next academic year".
They can expect their student support and capital maintenance grants for the same period to be maintained in cash terms, he added.
But privately, principals believe their funding position has been misrepresented.
The 8.5 per cent projection, they say, is based on a comparison with last year's "indicative grant" figure, instead of the grant they actually received, which turned out to be pound;6.6 million more than colleges were told to expect.
If last year's actual teaching grant is used as a basis for calculation, this year's cut will be 9.94 per cent rather than 8.5 per cent, according to calculations by TESS.
This would make it the second year running in which colleges have suffered a cut in real terms of 10 per cent. Last year's reduction led to courses being closed and more than 1,000 jobs being lost.
At the same time, the government is urging colleges to maintain student numbers, and has made a commitment to provide a place in training, education or work for every 16 to 19-year-old.
"What we can assume this means, in effect, is that that additional pound;6m which came to the sector last year is not to be carried forward," said John Spencer, convener of the principals' convention of Scotland's Colleges.
"Colleges must have clarity on the actual budgets that will be available. We must ensure no further disruption for learners," he said.
David Belsey, EIS national officer for FE, said: "The government's use of planned spending figures rather than actual spending to calculate funding cuts has two main effects: it disguises the real level of cuts and it makes public funding of FE colleges less transparent."
NUS Scotland's president, Robin Parker, has also raised concerns over the level of student support promised in Mr Russell's letter.
By telling principals to plan for the same level of student support they received last year, the education secretary was not fulfilling his election pledge to improve student support - it was doing the opposite, said Mr Parker.
Delaying the publication of funding letters to colleges created "uncertainty and confusion" for students, he added.
"Prospectuses are as worthless as the paper they are written on if massive cuts to colleges result in cuts to those courses."
A Scottish government spokesman commented: "We said we would maintain student numbers and college student support and that is exactly what we will do. The cabinet secretary made clear in his letter to colleges that delivery is based on published Scottish Funding Council baselines for last year. There is no scope for misinterpretation."
The letter had been welcomed by the sector in helping it plan for the next academic year, the spokesman said. "In line with the timetable published in our consultation on college regionalisation, this month we will also confirm college regions, with their funding allocations to follow by March."
He added: "We are providing the best deal we can for colleges at a time when we are having to reduce many other budgets as a result of the swingeing cuts the UK government is making to Scotland's block grant."