Melbourne's massive Metro Tunnel project faces derailment if a Liberal bid to force provisions for a South Yarra station is successful, the government says.
The Liberals are moving a motion in the state's upper house that would revoke the minister for planning's responsibilities in the City of Stonnington.
At present, there are no plans or provisions for a South Yarra station as part of the rail project.
But the coalition says it would be "an act of bastardy" for the government to not build the Metro in a way that allows a future connection to South Yarra.
"That's consistent with what the planning panel pointed to and we believe we have a good reason to make sure that occurs," opposition planning spokesman David Davis told reporters on Wednesday.
The Liberals want to be able to give Stonnington the power to plan for the South Yarra station.
Public Transport Minister Jacinta Allan said on Wednesday that Mr Davis's move in the Legislative Council was designed to "unpick" the project.
"There is a risk that if this motion passes the upper house it will cause delay to this number one infrastructure project for our state that is unacceptable," she said.
Mr Davis has given notice of the motion for Wednesday.