The association says industrial action could involve as many as 20 colleges, while employers continue to insist there will be no improvement on the 2.3 per cent pay offer from the Association of Colleges.
ATL chairman Chris Wilson said: "Fifteen colleges have indicated that they wish to ballot for action in October. Ten colleges would support a strike and five say they would support action short of a strike. The ATL is becoming assertive. We are a reasonable union but the AOC has managed to find our boiling point."
The Association for College Management says 95 per cent of its members reject the pay offer although it will not take industrial action of the type which requires a ballot. The ACM, which is now affiliated to the Trades Union Congress, is refusing to say what form of action it will take.
General secretary Peter Pendle said: "We had a vote among our members. There was a 20 per cent response rate, which we think is pretty good, and 95 per cent of them rejected the 2.3 per cent pay offer. We have asked the AOC to open up discussions again.
"We will not be taking industrial action in the traditional sense because we are an association which puts the learner first. We are an association of managers, therefore it is our job to keep colleges running."
The AOC says it is sticking to its guns over the 2.3 per cent offer despite the threat that another union is likely to be taking action alongside the National Association of Teachers in Further and Higher Education.
"The offer put forward reflects what colleges around the country have told us is affordable," said Ivor Jones, director of employment policy at the AOC.
"Colleges have to meet their pay bills largely from their core funding, which remains at 90 per cent of 199596 levels."
It says colleges which made an "unrealistic" offer would risk redundancies and cuts in provision.