Under the proposed tax, which was debated in the lower house on Tuesday, electric and other zero-emission vehicle drivers will pay 2.5 cents for every kilometre travelled on Victorian roads from July 1.

A 2.0 cent per kilometre charge will also apply to plug-in hybrid-electric vehicles.

The tax is expected to raise $30 million over four years and is forecast to cost the average electric vehicle owner between $260 and $300 annually.

Treasurer Tim Pallas has described the tax as "modest", about half the rate of what other vehicle owners pay through the fuel excise.

He has said it will ensure electric vehicle drivers make a fair contribution to the cost of building and maintaining the state's road network.

It comes as Environment Minister Lily D'Amboriso on Saturday announced 20,000 subsidies of up to $3000 for new electric vehicle purchases under $69,000.

The first 4000 subsidies became available on Sunday.

As part of the package, the government will also spend $19 million on new charging stations and $10 million to expand its electric vehicle fleet by 400 cars over the next two years.

The government wants half of all new car sales to be electric by 2030.

Victorian Greens spokesman for transport Sam Hibbins described the incentives as "an attempt at a political fix, not a genuine climate fix".

"Labor's confusing approach of offering incentives for electric vehicles with one hand while increasing taxes on them with other will undermine efforts to reduce transport emissions," Mr Hibbins said in a statement.

"To properly tackle the increasing level of emissions from transport, the state government needs to ditch the EV tax while keeping and increasing the incentives for electric vehicles."

Opposition Leader Michael O'Brien described the proposed tax as "crazy".

"At the same time as the government is imposing a new tax on electric vehicles to make them more expensive, the government is also announcing subsidies for electric vehicles to make them cheaper," he told reporters on Tuesday.

"It's like turning on the air conditioner and the heater all at once. It just makes no sense."

Leading car manufacturers and environmental groups have also branded the plan the "worst electric vehicle policy in the world".

The tax is all but guaranteed to pass the lower house, where the Labor government holds a commanding majority.

But the government faces a fight in the upper house, where without the support of the opposition, it requires the backing of three of the 11 crossbenchers to pass legislation.

Key crossbencher Fiona Patten says she isn't opposed to a user-pay system for the state's road.

But she also doesn't want people to be discouraged from making the transition to electric cars.

"Fundamentally I think the levy is quite right, I have no problem with that, but I'm not sure that the subsidies meet the mark," she told 3AW radio.

Similar taxes are expected to be introduced in South Australia and NSW.

Australian Associated Press