Australian Treasurer Josh Frydenberg addresses state treasurers ahead of a COAG meeting at the Commonwealth Parliamentary Offices in Melbourne, Wednesday, October 3, 2018. Josh Frydenberg has met with his state and territory counterparts to discuss GST and other matters. (AAP Image/James Ross)
Federal Labor is hoping influential Senate crossbenchers deliver crucial support for a push to guarantee no state or territory will be worse off under new GST revenue carve-up arrangements.
State and territory governments - excluding Western Australia - are calling for an amendment to proposed legislation to introduce a 75-cent floor in GST payments.
But the Commonwealth is staring down the rare unity ticket of Liberal and Labor treasurers, arguing the legislative guarantee risks bogging governments down in a "parallel scheme".
Shadow treasurer Chris Bowen says he's looking at an amendment for a "no worse off" guarantee proposed by Victoria, ahead of advising his team how to proceed.
"That recommendation to the caucus will reflect the fact that I want to see the legislation passed but will also reflect the fact that I want to see the legislation improve," he told Sky News on Thursday.
"We'll engage in discussions with the Senate crossbench, and you know, these things have some way to go."
The GST floor would apply to all states and territories.
The federal government has offered $9 billion in top-ups over 10 years and at least an extra $1 billion a year in perpetuity to get the deal over the line.
Treasurer Josh Frydenberg insists all jurisdictions will be better off.
But all state and territory treasurers - excluding Western Australia - want this promise legislated.
WA Treasurer Ben Wyatt sympathises with the other states but doesn't necessarily believe the guarantee must be enshrined in law.
The calls by most of the treasurers came after they met in Melbourne on Wednesday, with the group suggesting they would also be lobbying crossbenchers on the issue.
Prime Minister Scott Morrison said the commonwealth doesn't need approval from the states and territories to make the changes, which will be introduced when federal parliament resumes in two weeks.
Mr Morrison added the government doesn't need to pass laws to make the changes, but wants to so they can't be unpicked in the future.
Mr Frydenberg said amending the coalition's proposed legislation, to ensure no state or territory would get a worse deal, would create "parallel systems".
"We don't want to run a separate set of books. We want to run a new system which will be bedded down in legislation," he told reporters in Melbourne.
© AAP 2018