Premier Mike Baird is being challenged to back legislation that would rule out charging patients when they visit hospital emergency rooms – a measure proposed by the federal government.

The ability for states to charge for emergency room access was announced by federal Treasurer Joe Hockey in this month's budget as part of the introduction of a $7 co-payment for visits to a doctor and related services.

"Watching events as they unfold": Mike Baird and Tony Abbott meet to sign a WestConnex motorway funding agreement following the federal budget. Credit:Chris Lane

The measure was presented as a way to stop patients avoiding the co-payment at a doctor's office by visiting an emergency room instead.

The day after the budget, Mr Baird told the NSW Parliament the government "will be ruling that out".