The Greens deputy leader, Adam Bandt, said cutting single parents' payments from January 1 had saved the government more money than it had raised so far from the mining tax.

''Labor's talk of modern families rings hollow for single parents and their children who have been pushed on to the dole and into poverty,'' Mr Bandt said on Sunday. The proposal, which has been costed by the Parliamentary Budget Office, would cost the government $360 million a year, an amount Mr Bandt said could be covered by toughening up the mining tax.

It would pay a tax-free fortnightly supplement of $80 to single parents with a child aged under 16 who are receiving the unemployment payment Newstart. Those parents would also be able to earn more income from work before their payments were affected.

The government is saving $728 million over four years as a result of its decision to move about 84,000 people from the higher-paying single parent payment to Newstart. The difference between the payments is about $60 a week.

The change also curtails the amount of work people are able to do because of the different rules governing the single parent and unemployment payments.

The Greens announced last week that a formal alliance with Labor was over, with the party leader, Christine Milne, saying she had made the decision because the government had given too much ground to resources companies in the formulation of the mining tax.