Bill Shorten's role as the Australian Workers Union (AWU) boss has been called into question again with allegations an enterprise bargaining agreement (EBA) he signed off on was never actually endorsed by the workers in a vote.

A former worker from the Melbourne construction company Winslow Constructors told the ABC the 2004 EBA — negotiated when Mr Shorten led the union and signed by him — raised alarm bells with staff because it had pages missing when it was shown to them.

"[Page] 15 and 16 which I do know and still know, they weren't there," Winslow leading hand Brandon Ngaira told 7.30.

"They weren't in the EBA when they handed it to us."

Mr Ngaira said the workers noticed this because the pages related to inclement weather and rostered days off and the workers were forced to work on "forty-plus" degree days without water.

He said the missing pages were being discussed by employees when they were summoned to Winslow's head office in Melbourne to vote on the EBA.

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He and other former Winslow workers who spoke to the ABC anonymously, to protect their livelihood in the construction sector, said they were asked to stand in front of the company bosses' windows and to indicate whether they supported or opposed the proposed agreement by moving to the right or left respectively.

Mr Ngaira said, at first, the workers joked they should wave to the bosses through the windows, but then became angry.

"There were guys that were actually swearing and cursing and saying 'this is not right'," he said.

He said he believed some moved to the union and company side because they were fearful they would lose their jobs.

"I think guys were kind of threatened and thinking, if we go and stand on this side, will we be tarnished?"

Mr Ngaira and four other employees who did not know him confirmed the vote was not successfully carried that day.

They said the AWU told them there would be another vote.

Mr Ngaira said the second vote never happened.

But the EBA was lodged with the then-Industrial Relations Commission and signed by Mr Shorten.

"The contents and spirit of this agreement are endorsed and supported by the employees and management of Winslow Constructors Pty Ltd," the document signed by Mr Shorten read.

When asked if it was endorsed by the employees, Mr Ngaira replied "no".

"It's been signed, yeah, I'm not sure how it was passed," he said.

Shorten grilled over paid AWU membership fees

The AWU organiser at the Winslow EBA meeting was Peter Smoljko.

Mr Smoljko provided a statutory declaration to the Industrial Relations Commission stating the "agreement was genuinely approved by a majority of employees".

Mr Smoljko has left the union and is now a senior industrial relations manager with Winslow.

Winslow has already been under the spotlight in the Trade Union Royal Commission for admitting to paying its workers' membership fees to the AWU in return for, it's alleged, lower wages and conditions.

The Royal Commission was provided documents from Mr Shorten's tenure as leader which showed the union dues were paid by Winslow.

Mr Smoljko admitted to the royal commission the company paid workers' union fees, changing the transaction on records to look like an occupational health and safety expense.

Education Minister Christopher Pyne grilled Mr Shorten in Question Time on Thursday about the Winslow deals.

"He needs to answer what did Winslow Constructions receive in considerations for the $38,000 of payments to the AWU that they made when he was the Victorian state secretary?" Mr Pyne said.

The question being asked is whether Winslow workers lost out in wages or conditions.

Payment to AWU may offend Fair Work Act: lawyer

The ABC has analysed the 2004 Enterprise Bargaining Agreement for Winslow and those of five key competitors in Melbourne's civil construction industry in the same period.

Winslow paid its workers the lowest wages, and all other entitlements like leave and overtime were the same or worse than the other deals.

A senior industrial relations lawyer also questioned the legality of a 2005 payment by construction giant Thiess John Holland to the AWU under Mr Shorten's leadership when he was negotiating the $2.5-billion East Link toll road in Melbourne.

In 2006/07 a total of $190,875 was paid to the Victorian and National branches of the AWU.

In 2007/08 a further $20,917 was paid to the state branch.

"There's a very large payment to the union one would have hoped that was fully disclosed to the union members," Jeffrey Phillips SC said.

"Otherwise it just does raise very serious questions in relation to the propriety or the appropriateness of such a thing, also whether there was a serious conflict of interest."

Mr Phillips said there may be aspects of it which "offend parts of the Fair Work Act".

"Or [they] may even offend, at its very worst, aspects of the Crimes Act with respect to matters such as misleading statements of a dishonest kind — if these weren't matters told to members," he said.

"Or indeed it might even amount to a secret commission. And a secret commission is a matter which is very much under the province of the criminal law."

Shorten brings forward royal commission appearance

Mr Shorten would not speak to the ABC on Thursday, but frontbench colleague Richard Marles was keen to defend him.

"There is no question to answer here, other than to say this is precisely the kind of thing that enterprise bargaining was designed for and this is an absolutely quality agreement," he said.

Mr Shorten wants to defend himself at the royal commission and has asked it to bring forward his appearance there.

He will now answer any outstanding questions there on July 8.

"Bill Shorten needs to take his appearance at the royal commission very seriously," Jeffrey Phillips SC said.

"This won't be like Parliament where he can bluster his way through. It will take a lot of preparation. He'll be asked very precise questions and he'll need to focus and he needs to be very careful."