Labor heavy-hitter Alannah MacTiernan has moved to block a federal government attempt to defer a tribunal hearing over secret Perth Freight Link planning documents.

The North Metropolitan candidate, suspicious about the previously unannounced project appearing in the 2014 Budget and then surprising bodies such as Infrastructure Australia and the RAC, has since been locked in a battle to have the business case released under Freedom of Information legislation.

The 13 outstanding documents include emails regarding negotiations that went on between government ministers and agencies about the project, and the cost-benefit assessments and traffic modelling the government is referring to when it claims the controversial project is the best way to bust congestion in Perth's south.

The Australian Administrative Tribunal ordered the federal Department of Infrastructure and Regional Development to release the documents in 2015 and again in 2016, but the government appealed to the Federal Court, which has referred the matter back to the tribunal.