The commission has been looking into questionable deals between trade unions and employers, some of which took place during Mr Shorten's tenure as head of the Victorian and national branches of the Australian Workers Union (AWU).
He is expected to face questions over deals struck with employers while he was the state secretary of the AWU between 1998 and 2006, including a deal that the commission was told saved a cleaning company $2 million a year but was detrimental to workers.
They included payments of hundreds of thousands of dollars to the union between 2005 and 2008 by construction giant Thiess John Holland, described variously as "donations" or "other receipts" in disclosures to regulators.
The commission heard other examples where invoices from the union were charged for "training" but in fact related to the payment of membership fees, a practice the commission heard was used to boost member numbers.
And this man aspires to become the Pime Minister?