Treasury is warning the slump in business confidence and a cooling housing market could hit the government's books.
In its July update on the economy, the agency said there was a risk that growth could be weaker than forecast in the Budget in May.
The economy is forecast to grow about 3 percent a year on average over the next four years, with surpluses rising to more than $7 billion in 2022.
Treasury warned that may now be at risk.
It pointed out the latest set of indicators painted a mixed picture of the economy with wages continuing to grow strongly while retail spending weakened.
If that happened, the government might be forced to curb its spending plans, Treasury said.