The federal opposition leader, Bill Shorten, is set to be questioned the royal commission into trade union governance and corruption in August or September.

The inquiry has been examining the content of workplace agreements overseen by the Australian Workers Union, of which Shorten was national secretary from 2001 to 2007. He also was state secretary of the Victorian branch from 1998 to 2006.

It is understood the inquiry’s lawyers contacted Shorten’s lawyers late on Thursday about the next scheduled hearings in late August and early September, and that he confirmed he would be happy to volunteer attending.

In a statement, Shorten said he had always put the interest of workers first and had “zero tolerance for corruption or criminality in the workplace – whether you are an employer, employee or union representative”.



“Ever since the royal commission was established by the Abbott government, I’ve said I’d be happy to cooperate,” he said on Friday evening.

“I welcome the opportunity to talk about my 21-year record standing up for workers. I am proud of standing up for better pay, safer workplaces and decent conditions.”

Confirmation of the appearance before the inquiry came hours after the prime minister, Tony Abbott, said Shorten had questions to answer about deals the AWU entered into that may have shortchanged workers.

“I certainly think it would help if he would front the royal commission and clear things up,” Abbott said earlier on Friday.

Shorten’s successor as the AWU Victorian state secretary, Cesar Melhem, resigned as Labor’s whip in the Victorian upper house on Monday after allegations were aired at the royal commission about a 2010 agreement with a cleaning company, Cleanevent Australia.

The 2010 memorandum of understanding built on the pay rates that were enshrined in the 2006 enterprise agreement. The inquiry has been told the 2010 MOU required Cleanevent to pay up to $25,000 a year to the AWU on behalf of employees that were or would become union members.

An email tendered to the inquiry showed Cleanevent would have faced extra costs of about $2m a year if the enterprise agreement was not in place and the company had to employ workers through the 2010 modern award, which had much more generous penalty rate provisions.



Melhem denies wrongdoing. Abbott said the fact that Shorten’s successor as AWU leader in Victoria had quit a parliamentary post showed it was “obviously significant enough for Bill Shorten to at least offer us some answers rather than just delivering sermons”.

Shorten also faced questions on Thursday about separate claims that he had overseen a deal with a building company in which the firm agreed to pay employees’ union dues.

Fairfax Media reported that the AWU’s Victorian branch invoiced Winslow Constructors in 2005 for $38,228.68 to pay for 105 union memberships.

Shorten said he had always sought to improve workers’ pay and conditions and described Thursday’s newspaper article as “an unfair smear”. He said the agreement in question had delivered pay rises for the workers.

The education minister, Christopher Pyne, questioned whether workers at Winslow had been left worse off as a result of the deal. He said businesses were unlikely to pay thousands of dollars to the union unless there was a benefit to the businesses.

While pledging to cooperate, Shorten took aim at Abbott’s decision to set up the royal commission. The opposition leader said it was “truly appalling” that the prime minister had cut funding to important service delivery programs while he was able to find $80m “to smear his political opponents”.



“Tony Abbott’s abuse of taxpayers’ money to serve a political agenda won’t deter Labor from the fight for fairness,” he said.



“I will not be responding to matters that are being considered by the royal commission until I am able to appear.”