The University of Sussex has been accused of privatising more than a tenth of its jobs.
The institution has announced plans to outsource 235 positions to two private companies to manage its estates and facilities and provide campus catering and conferencing.
The University and College Union said it was not consulted on the plans announced to staff on Wednesday.
It said it will oppose them and is consulting its members. The transfer is planned for August 2013.
Unison and Unite, which also represents affected staff at the Falmer campus, has had meetings with members.
UCU general secretary, Sally Hunt, said people’s working conditions would suffer under a private employer.
She said: “Our position is that it is privatisation because it is taking people’s jobs funded by the public sector and transferring them to a |private employer.
“There is no doubt if these people become employees of a private company their working conditions will change significantly.
“UCU will oppose this. This news was sprung on the unions without any prior consultation or any discussion about finding solutions in-house.”
The staff will be transferred on their current terms and conditions under national regulations, but unions say it will not protect them “indefinitely”.
Ms Hunt said: “Once the employer has a business case to alter the terms and conditions they can do it, while I have no doubt new staff will be given inferior terms and conditions.”
The university, which employs 2,200 people, said it wants to cater for a growing number of students.
Student numbers have grown by 2,000 to 12,000 in the past two years and it expects to reach 15,000 by 2015-16.
Annually, the university takes in £170 million, of which about £45 million comes from Government.
However, John Duffy, registrar and secretary, said the plans were not due to cost but to increase quality.
He said: “As we grow, we need to ensure we provide support services to our students and staff as efficiently and effectively as possible – making best use both of public funding and, increasingly, of our students’ own investment.
“As one part of doing this, we are now looking to work with specialist external organisations to manage our estate and facilities and to provide our catering and conferencing services. These are areas where there is already a range of experienced, specialist, external organisations.”
One worker, who would be affected by the changes, said she fears for her job in the long-term.
The woman, who does not want to be named, said: “We are all gutted. This is not a time to be out of a job.”
However, the university said the plans are not about cutting staff.