Members of Victorian Tippers United brought traffic to a crawl when they slowed down to 15km/h on Melbourne's West Gate Bridge.

The bridge is one of the main arteries between the CBD and the city's industrial suburbs in the west.

The convoy was heard honking horns through the CBD on the way to the Victorian Parliament, where they were expected to arrive.

Victorian Tippers United Treasurer Ricky Woolcock, who is driving in the convoy, said the Victorian Government promised a fuel levy to cover the cost of living three months ago.

"Our fuel is up to 50 or 60 per cent of our costs, and they've stuck us out to dry so we've decided to come for a drive into the city to show them we need this done," Mr Woolcock told 3AW.

"They've fixed our rate so we can't gain any extra money back for the extra expenses.

"Most guys at the moment are lucky to make about $60 of profit a day."

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Department of Transport spokesperson Chris Miller said the convoy had "a big knock-on effect" on traffic.

"We've got queues back up onto the ring road that go as far back as Boundary Road, and back out onto the Princes Freeway with queues back out to Laverton," he said on 3AW.