WA's business community is calling for a review of the Royalties for Regions program, claiming it is no longer affordable.

The Chamber of Commerce and Industry says it is not sustainable for 25 per cent of mining royalties to be set aside indefinitely but Nationals leader Brendon Grylls has warned critics to back off.

Mr Grylls was kingmaker after the 2008 election when both parties needed the Nationals to form government, and both agreed to implement the regional royalties program.

Five years on and the CCI's John Nicolaou has serious concerns about its long term future.

"The government simply can't afford to allocate a fixed percentage of a growing revenue base to one particular program," he said..

The fund is protected by legislation which requires 25 per cent of mining royalties to be set aside.

Mr Nicolaou points out that while revenue going into the fund has been steadily rising, GST payments to WA have been falling.

"Between 2009 and now, Royalties for Regions will get around double what it was originally allocated in the first budget so it does pose some challenges now from a financial perspective for the state government.

The CCI wants the state's economic regulator to review the Royalties for Regions program, and believes there is no time to waste after Western Australia lost its triple A credit rating.

Nationals leader Brendon Grylls is not interested in wholesale changes.

"I'm not willing to make legislative changes to the Royalties for Regions act," he said.

He says in the last budget, more than $500 million was cut from the program to help improve the state's bottom line.

The Opposition's Ben Wyatt wants Royalties for Regions money dipped into more often to pay for key projects, including an extra floor at the new children's hospital.

"We need to be much more open in how we spend Royalties for Regions money provided that there's a strong return for all Western Australians," he said.

Brendon Grylls is adamant the program will remain as is.

"Until my last dying breath I will defend Royalties for Regions," he said.

The Treasurer Troy Buswell says changes to the program will be ongoing but there is no need for radical reform.