WA will not sign up to NDIS reforms without knowing exactly how much it will cost, with Premier Roger Cook also backing State treasurers in demanding clarity on the future GST-carve up before debating changes to the disability support scheme. National Cabinet gathers on Wednesday to discuss ways to rein in the cost of the rapidly ballooning $40 billion National Disability Insurance Scheme. The meeting looms as a major showdown between premiers and Prime Minister Anthony Albanese after State and Territory treasurers on Friday resolved that they would refuse to discuss overhauling the NDIS until there was certainty on GST top-up payments. The payments — a feature of the 2018 deal that placed a floor under WA’s share of GST — are set to expire in 2027, threatening to blow a major hole in the budgets of the Eastern States. Speaking ahead of National Cabinet, Mr Cook said that he backed the position taken by Treasurer Rita Saffioti and her counterparts. “We can’t sign up to something where we don’t know what the cost to the states is going to be,” he said. “And it’s important that we have time to consider the full detail and understand what the impact on our budget will be as a result of any reforms.” Mr Cook said tweaks to the NDIS, future GST arrangements and cost-sharing between the Commonwealth and States over the broader health system were best dealt with as a “package”. “We need to understand the full impact of any reforms around NDIS,” he said. “In addition to that you’ve got a range of States that are worried about the extension of the no worse-off arrangements and we’re looking for a significant uplift from the Federal Government in relation to health care reforms. “So there are a bunch of policy items in this basket and it makes sense that we can review all those as part of a package.” Mr Albanese and Federal Treasurer Jim Chalmers have repeatedly vowed to protect WA’s GST floor of 70¢ in the dollar, which is set to rise to 75¢ from 2024-25. However, they have so far remained silent on continuing GST top-up payments to other States beyond 2026-27, which will be examined as part of a Productivity Commission review due before 2026. Originally forecast to cost about $6.7 billion over the eight years of the arrangement, persistently high iron ore prices mean they are now expected to cost closer to $34 billion. WA has benefited from tens of billions in additional GST distributions since the new system was put in place but Mr Cook said it was important to remember the fix “does not favour Western Australia”. “The GST delivers to WA its fair share of the GST contribution we make to the overall pool,” he said. “No other State gets less than 70¢ (per dollar contributed) for its GST. And so we are by far and away doing the heavy lifting in relation to contributions to the GST pool.” The results of a review of the NDIS, including almost 1300 pages of detailed analysis, were presented to the States in November. The West understands the results of the review - to be released on Thursday - will recommend a new model to fund not just the NDIS but also “foundational supports” for the millions of disabled people who are not on the scheme. The hope is that offering basic support — in particular to children with autism and developmental delays — will reduce the reliance on the NDIS, which has become the only option for most families.