The Baird government says it will block a bill that would allow scrutiny of the organisation delivering the $15.4 billion WestConnex motorway.

When the government transferred control of the toll-road to the Sydney Motorway Corporation, it also ensured information held by that agency could not be captured by freedom of information laws.

Labor's roads spokeswoman, Jodi McKay, on Thursday moved a motion in parliament that she would introduce a bill bringing the Sydney Motorway Corporation under the Government Information (Public Access) Act.

"It is the largest infrastructure project in NSW and it is occurring in absolute secrecy," Ms McKay said.