The latest worsening of the budget deficit, to be revealed by Treasurer Scott Morrison on Tuesday, could be plugged by abolishing a handful of what the Greens claim are "unfair tax breaks".

Research by the independent Parliament Budget Office, conducted for the party, found the government would be $38 billion better off over four years if four entrenched tax lurks, including negative gearing, capital gains tax discounts and public subsidies for fossil fuels, were abolished.

Greens deputy leader Adam Bandt says the government needs to stand up to the very wealthy and wind back unfair tax breaks. Credit:Andrew Meares

The PBO's projection was also based on a scenario where Australia's flat rate 15 per cent tax on superannuation contributions was replaced with a progressive system in which the top rate would be 30 per cent on contributions above $150,000 a year.

The $38 billion that would be raised over four years by dispensing with tax breaks would almost exactly cover the latest blowout, to be announced by Mr Morrison on Tuesday.