SA premier should 'grow up' on GST debate

West Australian Premier Colin Barnett has lashed his South Australian counterpart for saying a possible change to the GST carve-up formula could see WA "rob" smaller states.

The Commonwealth Grants Commission, which decides what each state gets, is reportedly considering using a "lagged five-year moving average" for iron ore prices rather than a three-year average.

That would inject $547 million into WA's coffers in 2015-16.

With the steep drop in the iron ore price, it would be warmly welcomed by the state that receives just 35c for every dollar of GST it pays.

Mr Barnett was far from warm, however, when asked about SA Premier Jay Weatherill's response to the possible change.

Mr Weatherill accused WA of "moral bankruptcy" - a term he has previously used to describe WA's long-running campaign for a bigger share.

"I say `grow up, just grow up'," Mr Barnett said. "This needs to be a mature debate.

"To Jay Weatherill ... get over it. Start engaging in a sensible economic debate."

Mr Barnett said the five-year option would provide a more stable revenue stream but WA would not give up on its bid to have GST distributed on a per capita basis.

"We will not resile from long-term reform," he said.

He was supported by the federal MP for Perth, Labor's Alannah MacTiernan, who said NSW and Victoria would go "completely feral" if they were in the same position as WA.

Senate crossbencher David Leyonhjelm also backed a carve-up change, saying "WA gets seriously screwed".

But Greens leader Christine Milne said the rest of the nation should not be "caving into Western Australia".

Prime Minister Tony Abbott was non-committal, saying the commission's options would be dealt with "in the fullness of time".

Opposition Leader Bill Shorten followed suit, saying politics of the day should not determine the long-term future of federal-state relations.