Lecturers' unions are threatening to take Oxford Brookes University to an employment tribunal, after the increasingly bitter pay dispute took a new turn.

With the university ready to suspend the pay of staff who fail to provide examination marks, unions have accused the university of proposing to act illegally by breaking employment law.

And they have warned that unless the threat to withhold pay is withdrawn, it will seek compensation at a tribunal.

In a strongly worded letter NATFHE and the Association of University Teachers accuse Brookes Vice-chancellor, Prof Graham Upton, of mounting "a totally unwarranted" attack on teaching staff. And the unions say they are ready to escalate the industrial action.

Regional official Sue Davis wrote: "The combination of 100 per cent pay deduction and the imposition of a local pay award will do nothing to enhance the reputation of Oxford Brookes University.

"To threaten staff in such a way when they are legally engaging in industrial action is just pure bullying and intimidation.

"The deductions you have threatened bear no relationship to the action currently undertaken by our members, they are totally disproportionate.

"Not only that, but you have committed yourselves to non-payment of salaries when marking is returned."

The unions complaint would allege that the Brookes had acted contrary to the Trade Union and Labour Relations (Consolidation) 1992 Act, introduced by John Major's Conservative Government.

Some lecturers have refused to set, mark, and invigilate exams or coursework since March after their union's demands for a 23 per cent pay rise over three years were rejected.

NATFHE and AUT union members met at Brookes this week to discuss the university's promise to suspend the pay of anyone who had not submitted marks by yesterday.

Union officials made clear at the meeting that industrial action would continue and said they may also target other key university events.

They warned Brookes that they would face a national academic boycott if the "lock-out" of staff went ahead.

NATFHE's branch chair, Alan Reeve, said: "This decision shows how badly the university has misjudged the mood of academic staff who were outraged at the university's threats."

AUT's local association president, Angie Pears, added: "Staff deeply resented the heavy handed approach of the university and this vote confirms the strength of feeling at the meeting to continue our action."

In a letter sent to all staff last week, the university said it would implement the 12.6 per cent pay offer from August as it was the maximum it could afford.

Deputy Vice-Chancellor Rex Knight said marking and submitting students' exam papers was a contractual duty for lecturers.

He added: "There is absolutely no foundation in the unions' assertion that this institution would 'lock out' any of its staff and prevent them from working.

"We are doing everything we can to work with the unions to find a solution to the on-going dispute.

"While we are striving to resolve these matters, we are very concerned about the impact that the unions' action could have on students expecting to graduate this year."