The Napthine government has blocked a Senate order to produce documents on the multibillion-dollar east-west tunnel project, saying it would damage federal-state relations.

On December 2, the Greens successfully moved a motion in the Senate requiring Infrastructure Australia to produce the state government's tunnel submission, including the secretive business case, to the body by December 11.

Since the project's announcement, the government has repeatedly said it could not reveal the details for reasons of commercial confidence.

Infrastructure Australia national infrastructure co-ordinator Michael Deegan last week wrote a letter to Clerk of the Senate Rosemary Laing, urging reconsideration of the request. He quoted this advice from the secretary of the Victorian Department of Transport, Planning and Local Infrastructure, Dean Yates: ''Disclosure may prejudice federal-state relations, and inhibit disclosure of further commercially sensitive information to IA [Infrastructure Australia] and the Commonwealth.''

Mr Yates said the project was in a ''highly commercially sensitive period''. He said if the information contained in the short-form business-case materials provided to Infrastructure Australia became publicly available, it would ''likely result in extreme prejudice to the state's commercial position with respect to this tender process and other adjacent commercial toll roads''. He said they were cabinet documents, ''which obviously attract executive privilege and public interest immunity''.