The West Gate Tunnel doesn't open until 2022 but the planned rising cost to motorists is already at the centre of debate.

Liberal and Greens MPs have slammed the tolls, which are increasing each year despite the tunnel not even being completed.

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And even some Victorian Labor MPs have regrets about the size of the tolls.

"No one wants to pay more tolls but unfortunately that is the way it is to get the project built," Labor's Cesar Melhem said.

The Liberals and the Greens are on the same page about the tolls, which will rise by more than 4 per cent every year until 2029.

"This isn't Labor's plan. This is Labor's scam," Opposition Leader Michael O'Brien said.

"This sweetheart deal has been a bad deal from the start," state Greens Leader Samantha Ratnam said.

Victorian Greens Leader Samantha Ratnam called the tolls deal "bad from the start". Credit: AAP

In 2015 the nominal tolls were $2.75 for a regular trip, and $4.40 during the morning peak.

But by the time the tunnel opens in 2022, the tolls rise to $3.52 and $5.64 in peak hours.

Under the deal with the government, tolls will rise by 4.25 per cent every year until 2029 and then by inflation.

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Private tolling company Transurban has estimated first year revenue at $217 million, or almost $600,000 every day.

"This is an absolute gold mine for Transurban shareholders," Opposition Leader Mr O'Brien said.

Crews at work on the West Gate Tunnel construction site in Yarraville in June. Credit: AAP

The government argues it's just being transparent with the toll deal.

"People want to know. People want to have a sense of what the tolling prices will be," Transport Infrastructure Minister Jacinta Allan said.