Lecturers locked in a pay dispute have been told to mark students' exams within nine days or lose their pay.

Staff at Oxford Brookes University were given the ultimatum yesterdaymay16 as final-year exams got under way.

More than 6,000 final-year students at both of Oxford's universities have been told their results could be delayed because of industrial action which has seen lecturers refuse to set, mark or invigilate exams and course work since March.

Unions, including the Association of University Teachers (AUT) and the National Association of Teachers in Further and Higher Education (NATFHE), have demanded a 23 per cent pay rise by 2009 and have rejected a 12.6 per cent increase over three years.

In a letter sent yesterday, Brookes staff were told that the 12.6 per cent offer would be implemented and that employees who continued the strike after May 25 would have their pay suspended until they submitted the marks.

Deputy Vice-Chancellor Rex Knight said the university supported the case for better pay but did not support the national unions' action in withholding exam marks.

He said: "This raises the prospect that some students may not be able to graduate this summer. This is a very serious situation and we have to do all we can to make sure that we meet our obligation to our students."

One senior lecturer from Brookes, who did not want to be named, said staff were very concerned by the move.

He said: "We are extremely furious and extremely frightened.

"I think we are going to have to continue the strike, but it is going to be very difficult for people with mortgages and families."

Staff at Oxford University are also taking part in the industrial action, and Terry Hoadok, their AUT representative, said there was a real danger of students' papers not being marked if employers failed to return to the negotiating table.

He added: "This is a very difficult situation. We have said repeatedly that we do not want to harm our students' progress but this is the only way we can put pressure on our employers."