An urgent court action threatens to disrupt the billion-dollar WestConnex project and add more than $80 million to the final price tag.

Listed property company Desane Group filed a short service order in the NSW Supreme Court this week accusing the NSW government of trying to unfairly seize a Rozelle property.

The WestConnex proposal includes a plan for the acquisition of a property on Lilyfield Road, Rozelle.

Joined to the action was Roads and Maritime Services and the Sydney Motorway Corporation, the principal agencies behind the government's signature infrastructure project, WestConnex.

At the centre of the dispute is a 5200 square metre triangle of land in Rozelle, on Lilyfield Road. The Desane Group has grand plans for the site, including 200 apartments with views of the city and Blackwattle Bay and 1800 square metres of retail and commercial space.