RAILCORP has stopped employing overnight security officers for much of the week, in a development criticised for compromising safety on Sydney's train system.

Sydney's train operator told its security division this month it would only roster staff later than midnight on Thursday, Friday and Saturday nights.

Night patrol ... but not all the time. Credit:Jon Reid

The new rosters, which mean there will be no RailCorp transit officers employed at stations or on trains past midnight from Sunday to Wednesday, were criticised by unions and the state opposition yesterday for weakening security coverage.

''It is a concern, because previously there's been transit officers 24/7,'' said an officer for the Rail, Tram and Bus Union, Helen Bellette. ''That's been for the protection of customers but also for staff, particularly cleaning staff and especially in regional areas.''