Bill Shorten should offer the Australian people a full explanation of his conduct as a union leader if he wants to have the credibility and standing to be our next prime minister. As it now stands, his conduct, ethics and character are under serious question from some of the deals that were made by the Australian Workers Union when he ran it.

In particular, Mr Shorten must detail his knowledge of and involvement in a deal that resulted in $300,000 being paid to the AWU by Thiess John Holland in the mid- 2000s. The payments were part of a secretive "side-deal" on the EastLink road project. Executives from Thiess John Holland last week told the trade union royal commission that the payments were recorded on fraudulent invoices that disguised their true purpose.

Diary notes from one of the executives, Julian Rzesniowiecki, indicate it was Mr Shorten who had first suggested the payments, and asked for the builder to pay for four staff. That would have been worth more than $1 million to the AWU over three years. It was later negotiated down to $300,000.

Mr Shorten has denied any knowledge of the issuing of bogus invoices. He is at pains to say he did not agree to any deal. But the diary notes indicate he put forward the idea. It is hard to believe he was unaware of the large sums of money paid to the union after his offsider, Cesar Melhem, concluded negotiations over the side-deal.