Opposition Leader Tony Abbott has repeated his call for Julia Gillard to declare her confidence in embattled Labor backbencher Craig Thomson.
Fair Work Australia reportedly has made adverse findings against key officials of the Health Services Union (HSU), including its former national secretary Mr Thomson.
Mr Thomson, the union's president Michael Williamson and national secretary Kathy Jackson were told last month that FWA intended to make adverse findings against them, Fairfax reports.
They have been given several weeks to respond to the allegations and the workplace regulator will release its final report after considering their responses.
Mr Williamson said the allegations were "bread and butter stuff" while Mr Thomson said the newspaper had an "unreliable source".
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FWA has been looking at allegations involving the union officials since April 2009, but a formal investigation did not start until March 2010.
Mr Abbott told reporters in Melbourne on Friday the length of time it had taken to investigate the matter was "scandalous" and it should be concluded as soon as possible.
"But this is not just an issue for Fair Work Australia," he said, adding it was an issue for the prime minister.
"In the light of today's reports I call on the prime minister to stand up before the cameras and declare whether or not she still has full confidence in Craig Thomson."
The minority government depends on Mr Thomson's vote in parliament to survive.
Ms Jackson said any allegations against her were without foundation and she was not aware she was being investigated.
