For the first time motorists parking in short-stay spaces in Melbourne will pay a congestion levy as the Napthine government scrambles to find extra cash for new infrastructure without pushing the budget into deficit.

In another announcement before the state budget on May 7, Treasurer Michael O'Brien said the levy on 52,000 long-stay city spaces would rise from $950 a space a year to $1300 in 2013-14.

And for the first time the levy – which was branded a revenue grab by the Coalition when in opposition – will apply to about 20,000 short-stay city parking.

The increase, and the application of the levy to short-stay spaces, means revenue from the tax will rise from about $46.8 million in 2012-13 to about $91 million in 2013-14.

Mr O'Brien said it was a sensible move that would help fund major investments in road and public transport projects in the upcoming budget, with more than $300 million in new public transport upgrades already announced, including new trains, new train stations and level crossing upgrades.

He said the impact on cost of living pressures would be minimal, given a high proportion of spaces in the city were used by corporations rather than individuals and given it would fund improved roads and public transport.

"That is a very small contribution to more than $300 million of new transport projects already announced in this budget, and can I say there will be much more to come – more road project announcements, more public transport announcements," Mr O'Brien said.

When in opposition Coalition MPs were scathing about the levy, which was introduced by the previous government to discourage people from driving into the city, with Attorney General Robert Clark describing it as a "flat-out tax grab" and Health Minister calling it a "massive tax slug, pure and simple".