Further education colleges could lose up to 150,000 hours a week of their staff's time after lecturers introduced a work to rule.
The action, taken in protest against a 2.3 per cent pay offer, threatens to hit college finances by hampering student recruitment as well as data collection required by the Learning and Skills Council.
Union leaders say that if the work to rule continues into next year it could jeopardise proposals for reforms in the sector contained in a paper launched by education secretary Estelle Morris last month.
Natfhe, the college lecturers' union, expects other unions including Unison to join the action in pursuit of a pay rise at least equivalent to that received by school teachers - estimated to be worth 5 per cent.
A one-day strike is planned during the Labour Party conference in October.
Lecturers have been given model letters to hand to managers explaining that they will not work longer than their contracted hours and asking for their tasks to be prioritised.
Barry Lovejoy, head of Natfhe's colleges department, said it was expected that administrative work, including data collection, preparation for inspections, and implementation of reforms, would be affected the most.
More than 30,000 lecturers who belong to Natfhe work an average five hours a week over their contracted time.
Employers' representatives said they would be concerned if the threatened action affected colleges' income.
Ivor Lewis, director of employment policy for the Association of Colleges, said the pay offer was based on affordability and could not be increased without extra funding from the government.
"We are hoping that this week's spending announcement will shed light on how we may address this issue," he said.