The move has been condemned by the Educational Institute of Scotland's College Lecturers' Association as "an attempt to privatise a significant part of the public education service". Pay and conditions will deteriorate, the union warns.
The agency has in turn accused the CLA of "peddling the same myths as NATFHE in England". The further education lecturers' union south of the border has been in a long-running dispute with ELS.
Aberdeen College, Scotland's largest, confirmed this week it is not renewing fixed-term contracts for 500 staff and will only re-employ those it needs through the agency. ELS has recently opened an office in Stirling, close to the Association of Scottish Colleges, which represents the employers.
Rae Angus, Aberdeen's principal, said part-time staff would have to become self-employed and work through ELS. The number of full-time lecturers employed by the college is to be increased by 50.
Mr Angus said: "We need to have a degree of flexibility in employing people but we are not doing this to make savings per se. We depend on temporary staff for quite a high proportion of our work. Some courses are up 20 per cent and others down 20 per cent and we need flexibility."
At Falkirk, 120 temporary staff are in a similar position. Maxwell Sharp, the college's depute principal, said the majority would be re-engaged. "There has been no collapse in demand for part-time staff," Mr Sharp said.
A campaign to resist the use of employment agencies is now being mounted by the CLA. Joe Eyre, the association's president, said: "We will be encouraging members to exercise their employment rights by reference to an industrial tribunal if they are infringed. They will be forced to sign up with an agency on inferior pay and conditions. That is the experience from England."
Geoff Lennox, ELS's managing director, said: "Out of 154 colleges in England where we are operating, only two effectively reduced the hourly rate because of their severe financial difficulties. That is a tiny proportion. It was either reduce the rate or make people redundant."
Mr Lennox said Scottish lecturers would continue to be paid their current rate.