Prime Minister Malcolm Turnbull has refused to say whether company tax cuts will be included in the May 3 budget.

But there will be important tax changes, he told ABC radio on Tuesday.

The budget has been brought forward one week to give Mr Turnbull sufficient time to call a double-dissolution election if the Senate rejects government legislation restoring the building industry watchdog and toughening penalties for union corruption.

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Mr Turnbull said the government was carefully making decisions, citing the debate over changing the GST.

“It’s not because of politics, it’s because of economics,” he said.

The government came to the view that once you compensated people on low incomes the money left over with to provide tax relief was relatively small.

Finance Minister Mathias Cormann said Australians will know the Coalition’s tax plans in good time before the election, but conceded a July 2 poll could be called the week after the budget.

It would mean a seven week campaign.

“That’s a longer campaign than is usually the case in Australian politics so people will have more time than they normally would have to actually properly assess the ins and outs of our proposed tax policy,” he said.

Mr Cormann would not confirm company tax cuts, but said the aim of the budget was to make the tax system more growth-friendly.