Glyn Jones, principal of Pembrokeshire college, is warning that students aged 16 and upwards will be affected and fforwm, which represents Welsh colleges, says many programmes will come to an end unless other money is found.
"This could undermine the Assembly's ambitions to widen participation and tackle social exclusion," a fforwm spokesman said. "European funds have played a fundamental part in the sector's efforts to do this. Colleges have already scaled down EU-funded activity, but progress has been complicated by the freeze on core budgets.
"The sector has endured two years of zero growth, with all additional funding reserved for the FE pay initiative."
A report commissioned for the adult learning body Niace found European Social Fund (ESF) money helped almost 167,000 learners from 2000-4 aged 16-24. Around 55,000 benefited from schemes designed to improve training and education and promote lifelong learning.
In total, pound;64 million of ESF has been approved for lifelong learning projects since 2000. Colleges must show that the money will go on "value-added" projects and demonstrate they are doing something distinctive and different.
It can be a broad remit - from helping entrepreneurs to supporting those with learning needs. At Pembrokeshire, EFS money helped fund an incubation unit for small businesses run by students, offering premises and support until they can stand alone.
The college's projects are designed to be phased out, if necessary, when money dries up. The dilemma for learners, tutors and administrators is that no one knows what will happen next.
An all-party Assembly group on adult learning met last month and a group was set up to examine the problem. But the EU's decision on funding may not come for another year. The professionals' best guess is that from 2007, ESF will be 50-60 per cent of current levels.
Pembrokeshire college, with 12,000 students, 2,000 full-time, has used around pound;10m of ESF for capital and revenue projects, targeted at learners from 16 plus.
School leavers are among those benefiting from an ESF-backed one-to-one learning support programme "We screen students on entry to determine if they have dyslexia or numeracy problems," said Mr Jones. "But there isn't mainstream funding for that level of support. It will go."
Innovative projects to teach 500 disabled students independent living skills also face being axed.
"These were due to run until 2006. But unless we can find funding they will fold," said Mr Jones.