The Association of University Teachers could take legal action if universities dock the pay of academics who took part in last week's strike by 1/260th instead of 1/365th.
The Universities and Colleges Employers Association has assumed that 1/260th should be deducted, on the basis of a five-day working week. The AUT claims this is a misunderstanding of the legal position.
Tom Wilson, AUT assistant general secretary, said court cases had established that the nature of an employee's contract was the key issue for deductions. Academics could on occasion be called on to teach outside their normal timetable, and were effectively available for research and scholarship at any time.
If staff were to confine themselves to working between 9am and 5pm from Monday to Friday, the system would instantly grind to a halt, Mr Wilson said.
"If the employers want our flexibility and goodwill, they have to pay for it. As a last resort, if they are really going to insist on deducting 1/260th, we are considering taking some test cases to the courts."
Mr Wilson said it was not yet clear how many institutions intended to deduct 1/260th. Many had not yet made up their minds, and some appeared to be making no deductions at all. Those who had decided on 1/365th included University College London, and Durham and Ulster Universities.
The AUT is also planning to boycott the administrative work involved in teaching quality assessment and lecturers may withdraw as members of assessment teams as part of the ongoing battle over pay. The union also intends to disrupt staff appraisal processes.
Letters have been sent to every vice chancellor in the old university sector warning them that pushing ahead with assessment could result in "long-lasting bitterness" and damage the integrity of the assessment process.
Lecturing unions in the new universities are working strictly to the letter of their contract. This effectively means withdrawing the goodwill upon which lecturers say many institutions rely.
A spokesman for the Higher Education Funding Council for England said that some assessments had been rescheduled already and that institutions experiencing problems should contact them. He said that assessments were not overly bureaucratic.
* Lecturers' union Natfhe members at the Manchester College of Art and Technology went on strike this week over four compulsory redundancies. The union claimed four staff had been victimised, but management labelled the dispute a "clash over 'jobs for life'". The industrial action on Monday was in response to the termination of four long-serving academic staff who taught engineering subjects.