Labor is demanding the employment minister explain why she did nothing about a breach of workplace laws by the head of the building and construction watchdog.
If Michaelia Cash can't, the opposition says she should resign.
Australian and Building Construction Commission chief Nigel Hadgkiss resigned on Wednesday after he admitted to contravening the Fair Work Act.
Senator Cash later told parliament she had known about the breach since October 2016, an admission Labor says is unacceptable.
"This is a minister who goes on in an almost incoherent manner, attacking the trade union movement day in, day out in parliament for alleged breaches of the law," opposition frontbencher Doug Cameron told reporters in Canberra on Thursday.
"She needs to answer why she's done nothing about this guy, why her hand-picked commissioner breached the law and she did nothing about it.
In court documents, reported in The Australian, Mr Hadgkiss admitted that in December 2013 he directed that Labor government changes to right-of-entry laws - which were due to come into effect in January 2014 - not be published by the agency.
The coalition won the federal election in September 2013, promising to repeal the laws.
Mr Hadgkiss met two senior staff on December 19, 2013, directing no changes be made to agency educational material to reflect the law because he believed it would be changed.
The laws are yet to be repealed.