College caretakers, technicians and other support staff have rejected management proposals for new flexible contracts. They are arguing for guarantees against possible exploitation.
The model contract from the Colleges' Employers' Forum calls for an average 37-hour working week, though staff could be asked to work 40 hours without overtime but with time off subsequently.
A spokesman for Unison, Britain's biggest public-sector union, said: "We are suspicious of how local managers will apply the flexibility they have in the contract." It was one of many clauses staff were deeply unhappy with, he said.
Roger Ward, chief executive of the CEF, said: "A growing number of CEF members have now reached a local settlement with support staff." A survey estimated around 30 per cent had reached agreements.