The findings by the lecturers' union NATFHE confirm its fears of a drive towards "casualisation", with an increasing number of colleges taking on part-time staff on a day-to-day basis through agencies rather than employing them directly on termly contracts.
College employers argue that the agencies, led by Nottingham-based Education Lecturing Services, offer flexibility and more control over costs.
The survey, answered by union branch secretaries at 99 FE colleges, showed 25 were already using agencies for their part-time staff and 21 were reported to be thinking of making the move.
The findings follow disputes at several colleges where employers have effectively sacked all part-time staff and then re-employed them on a day-to-day basis through agencies.
The Association of Colleges, the FE employers' organisation, has told its members that using agencies gives them greater flexibility and can help cut costs.
But NATFHE says staff usually face pay cuts and the loss of employment rights when they are taken on by agencies and are then deemed to be self-employed.
Sue Berryman, the union's FE negotiating secretary, condemned the trend. "Some of these part-time staff have worked for their colleges for 20 years or more and are then dismissed and forced to accept the poorest terms and conditions in the profession," she said.
Marcia Roberts, director of professional services at the AOC, said: "We endorse the use of third party providers as a useful tool."
ELS chief executive, Geoff Lennox, rejected NATFHE's claims.J"This is an old argument but there is absolutely no truth in it. Our staff are self-employed so they don't have the same terms and conditions, but we pay them the same or more than colleges."