Shorten must explain 'dud' deals: Abbott

Bill Shorten has a lot of explaining to do at the unions royal commission, Prime Minister Tony Abbott says.

Mr Shorten will front a hearing of the royal commission in Sydney on Wednesday to answer questions about payments made by a number of companies to the Australian Workers Union, which he previously led.

"There have been some deals that have been done to help the unions, but to dud the workers - let's see what light can be cast on that in the next day or so," Mr Abbott told reporters in Sydney on Tuesday.