Can my employer impose new charges for parking at work which will cost me £300 a year?

My employer is an academic institution which owns thousands of parking spaces across it's campus, all of which require a permit, which are free for staff but paid for by students. To reduce congestion the university have now decided to introduce barriers and charge all entrants, including staff. The scheme is designed to encourage car sharing and use of public transport amongst lecturers and staff and will involve swiping an ID card when a driver enters the campus. This will be recorded and charged per hour and deducted from wages. On average it will mean a £300 deduction per year for a full time member of staff. Our department (sports centre) involves shift one starting work at 6.30 in the morning, the other finishing at 10.30 at night. There are very few trains and buses at these times and our staff are spread over a large area which means car sharing is not really an option. Our salaries are only around £1000 a month, so if we drive to work it means a 3% drop in pay. Can an employer legally charge it's employees for car parking which they own themselves? I accept a small firm which does not have the facilities might charge, but should a major employer charge their own staff for the use of their facilities and is the change in our employment terms actually legal?