The Greens are prepared to team up with the Coalition to block an extension of Transurban's CityLink contract, in a move that could deliver the kiss of death to the West Gate Tunnel.

Victorian Greens leader Samantha Ratnam said the party was against the Andrews government's planned $5.5 billion toll road and would work with the opposition to stop it.

But Ms Ratnam also issued a warning to Opposition Leader Matthew Guy – who is promising to revive the East West Link if elected next year – that the Greens will not help to kill off one major toll road just to see another one built elsewhere in Melbourne.

"The Greens will do everything we can to stop these mega-expensive, congestion-causing toll roads," Ms Ratnam said.