The NSW parliament has ordered the release of all documents relating to the WestConnex motorway project, a move the government says puts the project at risk.
Labor and the Shooters Party joined forces to pass a Greens motion in the upper house on Tuesday, giving the O'Farrell government 21 days to release all draft and final versions for the project.
Those documents will include emails, meeting minutes and diary notes for WestConnex, which is the country's largest transport plan, linking Sydney's west and east.
Coalition government MPs labelled the motion a "spiteful" move that would see commercially sensitive information disclosed.
Roads Minister Duncan Gay said releasing the documents could cost more than $1 million.
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"This puts at risk the biggest road project in the country because people will lose confidence in the parliament of NSW," he told AAP.
"It destroys our economic position in getting the best deal for the state."
But Greens MP Mehreen Faruqi, who introduced the `call for papers' motion, said the documents would lift the lid on the government's traffic forecasting and home acquisition plans for the project.
"WestConnex is the largest infrastructure project in Australia, and yet the public has not seen the business case nor a detailed justification for why this is a priority," she said in a statement.
"All we've seen is a glossy executive summary with pretty pictures."
The opposition's roads spokesman Walt Secord said the call for papers was a win for openness and transparency.
"I fully support lifting the lid on the minister's obsessive secrecy around WestConnex," he said.
