Labor is promising to deliver bigger budget surpluses than the coalition if it wins the next federal election, by matching any new spending commitments with savings measures.
Meanwhile, the prime minister has left the door open to bending the economic golden rule if circumstances demand.
Shadow Treasurer Chris Bowen has seized on a supposed split in senior government ranks over the fundamental fiscal rule to offset spending against savings.
Mr Bowen said the "politically desperate" treasurer and finance minister were at odds over how to afford GST top-ups and extra Catholic and education school funding.
"They've thrown away the debt and deficit disaster and budget emergency and are just throwing money at their political problems," he told Sky News on Sunday.
"Josh Frydenberg has thrown away the rule book in his first couple of weeks as treasurer.
"Well I have a different approach. I believe in bigger budget surpluses and that requires those fiscal rules to be adhered to."
Mr Bowen said Labor would deliver "substantially bigger" surpluses than the coalition over the next four to 10 years.
"We've made those commitments and we've made the tough decisions to underpin them," he said.
Prime Minister Scott Morrison says he is committed to matching government spending with savings.
"But as with those rules in the past, where there are exceptions to the rules, the government reserves the right to exercise that discretion, but they are the rules," Mr Morrison told the ABC.
"When ministers bring forward proposals, they are required to bring them forward with offsets."
Australian Associated Press