The Royal Commission into Trade Union Governance and Corruption has unearthed new evidence in relation to allegedly secret deals struck between the Australian Workers Union (AWU) and employers.

The inquiry has told the ABC it will this week put the new evidence to witnesses who are expected to be questioned about matters that arose earlier this year.

"More information has come to light since the AWU hearings began in late May [and] the commission has further evidence that it will put to the witnesses over the next four days," a spokesman for the royal commission said.

Federal Opposition Leader Bill Shorten was called to give evidence into the same matters in July and could be called again for cross-examination, although he is not listed as a witness.

Hearings today and Tuesday will focus on an arrangement between the AWU and a cleaning company, Cleanevent, under which the company was to pay $25,000 a year to the union in a so-called "side deal" to its main enterprise bargaining agreement.

As part of this "case study", the commission will today make public a statement it received in July from Paul Howes, who took over as national secretary of the AWU in 2007 when Mr Shorten entered Federal Parliament.

Mr Howes, who is not expected to be called to appear in person, has previously distanced himself from the "side deal", saying that as national secretary he signed off on the EBA only.

Later this week the commission will revisit a case involving Chiquita Mushrooms, whose EBA was negotiated by Mr Shorten for the AWU when he was Victorian state secretary of the union.

It has been alleged that the EBA left workers worse off than under previous arrangements.

Shorten 'will always stand up for workers'

The inquiry has heard allegations that the real nature of a range of payments to the union was disguised, including a donation from a construction company towards Mr Shorten's 2007 election campaign.

Mr Shorten defended his record as a union leader when he appeared at the royal commission.

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He has repeatedly criticised the inquiry as being politically motivated.

Late yesterday, a spokesman for Mr Shorten told the ABC the he had "acted in the best interests of workers on each and every occasion".

"He's proud of his record and will always stand up for workers," the spokesman said.

On Thursday, Cesar Melhem, who took over from Mr Shorten at the AWU in Victoria in 2006, will give evidence.

Mr Melhem, a Victorian state Labor MP, was forced to resign as chief whip in the Victorian parliament earlier this year as a result of adverse revelations in the royal commission.

This week's hearings will be the last big block of public sessions. Days have been set aside at the end of this month for further examination of matters involving the Construction, Forestry, Mining and Energy Union (CFMEU).

Since it began in March 2014, the inquiry has heard from more than 400 witnesses during 160 public and private hearing days in Sydney, Brisbane, Canberra, Perth and Melbourne.

The inquiry, set up by the Abbott government with former High Court judge Dyson Heydon as Commissioner, is due to report by the end of the year.