The Rail, Tram and Bus Union (RTBU) expressed on Friday its opposition to plans for the relaxation of fatigue standards for train drivers in New South Wales from the current 12-hour maximum.

The union warned that lives may be placed in danger if the train drivers work beyond their shifts. It cited a Monash and Sydney university analysis that removing shift limits was potentially dangerous.

The analysis, made by fatigue and safety expert Dr. Shanta Rajaratnam, said that after eight hours of exposure to a particular task during a shift, the risk of accident or an injury substantially goes up. He explained that a shift beyond 12 hours would not have enough opportunity for restorative sleep before the start of another shift.

The union called on the National Transport Commission (NTC) to reject the recommendation to extend the hours as part of a move to create a nationwide single national rail regulator. The lifting of the fatigue standard aims to achieve more flexibility and to reduce the burden and regulation cost.

"Our concern is that uniform legislation across Australia should raise standards across Australia rather than reducing them to the lowest common denominator," ABC quoted RTBU National Secretary Bob Nanva.

Fatigue risk management is included in an agreement between the federal and state governments in December 2009 to implement a national rail regulator. Ministers are scheduled to discuss the recommendations from the commission on May 18.

"In New South Wales there are some of the toughest rail safety regulations in the world and that is a product of several recent tragedies - including the Waterfall and Glenbrook rail tragedies - and as a result of the McInerny Inquiry which recommended tough fatigue standards," Mr Nanva said.

NTC Project Director Jeff Potter said he doubts if NSW trains drivers would work beyond their 12-hour shifts under the nationalised rail standards.

"They won't be working in any unsafe way because the requirements have been put in to ensure there's adequate time to rest between shifts, to ensure that time such as commuting to and from your work are taken into account and to require operators to make sure they've got adequate staff to safely run their rail operation," he told AAP.