Federal Treasurer Wayne Swan says next month's budget will involve some pain, but he is refusing to say whether it will include initiatives on paid maternity leave.

Mr Swan will deliver his first budget on May 13 and has pledged to deliver $31 billion in tax cuts while making significant cuts to government spending.

"It is going to be a tough budget, it is going to involve some pain, there is no doubt about that," Mr Swan told Fairfax Radio Network.

"We have got to put in place the settings, which not only put downward pressure on inflation, but also make the investments for the future so that we can lift the productivity of this economy and create wealth without creating inflation in the way in which we have in recent years."

The government was looking at the issue of paid maternity leave and has referred the issue to the Productivity Commission, he said.

The Community and Public Sector Union has called for six months' paid maternity leave to keep pace with international standards and provide support for working mothers.

'Balancing act'

And the ACTU says 14 weeksof paid leave would not hurt the budget.

"We understand that Australian women are performing a very difficult balancing act," Mr Swan said.

"They are increasingly participating in the workforce and participating in bringing up the next generation of young Australians, so they are deserving of support."

But he said there were "significant" cost implications for the budget.

"We have referred the matter to the Productivity Commission who is coming back to us later this year or early next year."

Mr Swan, when asked whether there would be anything on paid maternity leave in the budget, said: "I can't comment, one way or the other, when it comes to budget measures at the moment."