Labor says it is “quite remarkable” Employment Minister Michaelia Cash wasn’t aware of the extent of the wrongdoings of the head of the government’s building and construction watchdog before he resigned last week.

Nigel Hadgkiss stepped down as the Australian and Building Construction Commission chief last week after he admitted to breaching the Fair Work Act.

“The ABCC was created in December last year and Mr Hadgkiss was appointed as regulator of the ABCC even though legal proceedings of a serious nature were on foot about his conduct,” Labor employment spokesman Brendan O’Connor told Sky News on Sunday.

Senator Cash told parliament last week she had known about the matter since October, 2016, but denied it meant she knew of the breach until Mr Hadgkiss resigned.

In court documents, Mr Hadgkiss admitted that in December, 2013, he directed Labor government changes to right-of-entry laws – due to come into effect in January 2014 – not be published by the Fair Work agency, which he headed at the time.

Nigel Hadgkiss: out of a job.

The Coalition won the federal election in September, 2013, promising to repeal the laws.

ACTU president Ged Kearney said such actions strengthened the case for a national corruption commission.

“If ever you needed evidence, there it is,” she told ABC television.

“I would hate to see what she [Senator Cash] would say if the union movement made a similar action as to that.”

But Australian Chamber of Commerce and Industry chief executive James Pearson said Mr Hadgkiss, a distinguished and long-serving public servant, has resigned faced with these allegations.

He said there were many officials of the CFMEU who did not resign in the face of allegations and instead went out and ignored the law.

“Who have to be taken to court at considerable public expense, who are regularly found guilty, who are subject to fines totalling now in the tens of millions of dollars,” Mr Pearson told ABC television.