Crossbench politicians have launched a push to restore the auditor-general's funding in a bid to stop investigations being slashed by 20 per cent.
The Australian National Audit Office forecasts the annual number of audits will fall to 38 without a cash injection of $6.5 million to allow its target of 48 to be met.
The Greens have teamed up with independent senators Rex Patrick and Jacqui Lambie to amend a budget appropriations bill to restore the money.
Lower house MPs Zali Steggall and Helen Haines are also supporting the move.
Greens Senate leader Larissa Waters said it was no surprise the coalition was cutting the audit office's funding after it exposed scandals including sports rorts and the Western Sydney Airport land deal.
"Well hey presto, the Christmas gift they get is now they have to cut their audit capacity by 20 per cent," she told reporters in Canberra on Monday.
"How very convenient for a government that is allergic to transparency, that has been dragging its heels for four years on a federal corruption watchdog."
She accused the government of trying to muzzle one of the most effective transparency agencies in Australia.
Senator Patrick said the auditor-general was the bastion of government oversight.
"It is essential the auditor is allowed to continue the good work he does," he said.
Labor MP Julian Hill has commissioned Parliamentary Library research showing that by 2023/24 the audit office would have taken a 22 per cent cut since 2013.
"Nearly a quarter of the ANAO budget will be gone since this government was elected. That's a disgrace," he told reporters in Canberra.
"They're trying to hide their rorts, their waste."
Prime Minister Scott Morrison has argued it would be premature to increase the ANAO's funding before a review of its arrangements is finished.
Mr Hill wants responsibility for the auditor-general removed from the prime minister's office and reassigned to as a parliamentary department.
