Rating agency Moody’s has analysed Thursday’s budget and said its results were underpinned by very low rises in spending.

It said achieving the low spend assumed public sector employee costs rose by 0.9 per cent a year.

“Since these projections rely upon wage outcomes of 2 per cent, that is in line with the state’s wages policy, reductions in full time employee positions would be required to meet these targets,” the analysis said.

The state opposition seized on the report, and said Mr Gutwein should come clean on how many additional jobs would need to go.

“If Peter Gutwein is to achieve his much-touted surplus, he will need to significantly cut the public service,” Opposition Leader Bryan Green said.

“The Treasurer’s dodgy surplus is built on the false premise that public sector employee costs will rise by just 0.9 per cent a year.

“We know that’s completely unrealistic given the government will be forced to increase wages by at least 2 per cent.”

But Mr Gutwein said Labor had no credibility on budget matters.

“The two per cent wages policy in the budget is fully funded, and there will be no new job cuts,” he said.

“Moody's statement does, however, highlight the folly of the unions' three percent wage claim, which is being actively aided and abetted by Labor.

“The union claim would cost the budget an additional $180 million over the forward estimates which is the equivalent of 1,800 jobs.”

The public sector union has made a claim for a wage increase of 2.5 per, followed by an increase of 2.7