Proctors at Oxford University have fined graduating students more than £6,000 for their post-exam celebrations - with the help of the social networking site Facebook.

Following the fines, the university's student union has accused the proctors of a "disgraceful" intrusion into student privacy.

The sum of fines collected for "trashings" - the practice of graduating students spraying each other with Champagne, foam, eggs, and flour - was five times higher this year than last, thanks to evidence gathered online.

Fines ranged from £40 to £500.

The university has been attempting to rein in students' celebrations for decades.

In 2004, it issued spot fines of up to £70 for "fluid spraying or egg hurling" after residents complained that the clean-up bill ran to thousands of pounds. Only 14 students were caught.

Martin McCluskey, president of the Oxford University Students Union, said: "Students started receiving emails from university proctors, with links to Facebook photos. They have been given what amounts to an ultimatum: they can appeal, or pay a fine of between £70 and £100.

"We are particularly appalled by the timing. Many of the students have already finished their studies or are abroad and don't want to come back for the appeal, so they have been paying up."

The union has provided students with a set of instructions on how to alter their Facebook privacy settings.

Mr McCluskey added: "We don't condone any unruly, violent or disorderly behaviour, but university discipline procedures should be transparent.

"This isn't and we suspect it also is a breach of the Facebook users' code."

Barbara Hott, a spokesman for Oxford University, said: "The University Proctors have told the students that they are welcome to meet their friends after their exams, but that students who create a mess in the street with food or alcohol, or who indulge in antisocial behaviour contrary to university regulations, will be disciplined.

"Last year, the University Proctors received numerous complaints from university staff and members of the public about a significant minority of students taking part in antisocial behaviour that seriously affected those who live and work in the city of Oxford.

"Given these concerns, the Proctors took the steps available to them to identify and discipline the culprits.

"Where the University Proctors used evidence from Facebook, it was only publicly-available material.

"The fines collected each year go towards a good cause within the university.

"The Proctors for 2007-08 decided that the money from fines should be split equally between the Bodleian Library Redevelopment Fund and the Friends of the Pitt Rivers Museum."

Alex Hill, 21, a philosophy and mathematics student at Oxford University, was among students to receive a disciplinary email stating she had engaged in "disorderly" conduct.

She was shown links to three photos on Facebook where she was covered in shaving foam.