Attorney-General Nicola Roxon says the Fair Work Australia (FWA) investigation into the Health Services Union (HSU) has taken longer than the government would have liked.
But she says that's a matter for the FWA.
The workplace watchdog is expected to give an update on Tuesday on its investigation into the union's national office and former union boss Craig Thomson.
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FWA kicked off an inquiry into the union's finances in April 2009 but it did not became a fully-fledged investigation until March 2010.
It has been alleged a credit card in the name of Mr Thomson, who was the union's national secretary from 2002 to 2007, was used to pay for prostitutes, lavish meals and cash withdrawals.
Mr Thomson, who represents the NSW seat of Dobell and has been in and out of hospital due to illness in the past fortnight, has strongly denied any wrongdoing.
Ms Roxon said the timing of the final report was ultimately a matter for Fair Work Australia.
"It has taken longer than we would have liked," she told Sky News on Tuesday.
"But they're an independent agency, they can conduct their inquiries as they need to according to the law.
"I think there would be outrage if there was political interference in that process."
Liberal senator Simon Birmingham says the saga has dragged on for three years and the FWA report should be released as soon as it is finished.
"If this report is finished ... it either needs to be released publicly immediately or, if prosecution is to be pending, it needs to be referred to the Director of Public Prosecutions immediately," he told Sky News.
Former workplace relations minister Chris Evans echoed Ms Roxon's comments that the process had been conducted properly.
"Whatever their report finds, any action that flows from that will be a decision for the relevant authorities," he told reporters in Canberra.
"It's been a long process and I think everyone wished it had been quicker."
The Tertiary Education Minister said everyone involved in the allegations should be given the presumption of innocence until the FWA findings were made public and any potential prosecutions lodged.
