Shadow treasurer Chris Bowen has signalled Labor will push for an amendment but ultimately pass the Morrison government’s proposed GST floor without a safeguard that no state will be worse off.

On Wednesday, state and territory treasurers unanimously demanded the federal government legislate the safeguard, but were rebuffed at a meeting in Melbourne, with the Morrison government accusing the states of attempting to set up a “parallel” GST scheme to extract even more money from the commonwealth.

At separate press conferences the treasurer, Josh Frydenberg, and prime minister, Scott Morrison, pointed to current projections that no state will be worse off and called on Bill Shorten to help the Coalition pass the legislation despite states’ concerns.

Bowen responded that it was “arrogant” of the federal government to refuse to guarantee in legislation something that had been demanded by every treasurer, whether “Labor, Liberal, small-state, big-state, GST net recipient or net contributor”.

“Of course we want to see this legislation pass, and that will be reflected in my recommendation to the Labor caucus,” he told reporters in Sydney.

“But we also want to see a guarantee for the people of Tasmania, New South Wales and every other state and territory, that they won’t be worse off, and of course that will also be reflected in the approach that I recommend to the Labor party.”

Bowen said he was “optimistic” his recommendation – apparently to attempt an amendment for a safeguard but to pass the GST floor in any event – would be accepted by the caucus.

In June the federal government announced its plan to introduce a “floor” so no state receives less than 70% of their own GST revenue from 2022-23, rising to 75% from 2024-25. Over 10 years the policy will cost $9bn, of which Western Australia will get $4.7bn.

But Victorian treasury modelling suggests that in a worst-case scenario – depending on certain assumptions about mining production and property taxes – Victoria could lose up to $940m, New South Wales up to $1.1bn and Queensland up to $651m.

After the meeting the Victorian treasurer, Tim Pallas, said that “all states and territories” agreed that commonwealth assurances should be incorporated into legislation to guarantee their budget planning and prevent a potential “massive fall away in revenues”.

Pallas said the states would continue to lobby for the safeguard, noting the legislation has “still got to make its way through federal parliament”.

The Queensland treasurer, Jackie Trad, said there was a “real risk”, if the GST floor is legislated without a guarantee, that some states will be worse off.

The NSW treasurer, Dominic Perrottet, said the commonwealth was correct that on current modelling no state will be worse off, but under a number of “likely and probable scenarios” some states will lose out.

“What I don’t accept is change in the GST model which will make states worse off,” he said. “We believe this legislation will do just that.”

Asked why the federal government refused to legislate a safeguard if it believed all states will be better off, Frydenberg said the states want the commonwealth “to run a parallel scheme – the old system and the new system”.

Frydenberg said the commonwealth can change the GST “via legislation”, signalling the Coalition will push ahead with a bill for a GST floor without state agreement. That bill is now likely to pass, with Labor support.

The treasurer said there was “clear evidence” all states and territories will be better off, arguing they had “never had a more generous partner on the GST” than the Coalition government.

At a press conference in Perth, Morrison said the federal government was not in “the habit of writing blank cheques to anybody”.

“I’m used to states and territories trying to talk out more money from the commonwealth,” he said.

“It’s my job to protect Australian taxpayers and ensure that we deliver on our plan to ensure that every single state and territory is better off.”

Earlier, on 6PR radio, Morrison said the states were “trying it on” and claims they could be up to $1bn worse off were “rubbish”.

The prime minister derided assumptions in the Victorian modelling, suggesting they would be worse off only “if they stand on one leg, and they point towards Saturn … then turn around three times”.