The News Ltd Sundays carry this story from Sam Maiden.   A $100M Royal Commission headed by a former High Court Judge.

BRIBES, secret commissions, corruption and slush funds will be the target of a powerful royal commission into unions to be announced by the federal government on Monday.

Prime Minister Tony Abbott's strike against union corruption will include expanded terms of reference and the inquiry will have the power to compel union leaders to appear.

Former High Court judge John Dyson Heydon, 70, will be appointed to lead the royal commission.

The QC is a "black-letter law" conservative known during his time on the bench for his dissenting judgments and criticism of judicial activism.

The new terms of reference go much further than the inquiry promised by Mr Abbott into the Australian Workers' Union slush fund affair.

It will also extend beyond the Health Services Union scandal involving former ALP national president Michael Williamson and allegations that former Labor MP Craig Thomson used union money to visit prostitutes. He has pleaded not guilty to charges arising from the matter.

The royal commission will now consider "off the books'' transactions involving union leaders including secret commissions, kickbacks or bribes and organised crime links.

It follows allegations of organised crime links to the building industry, allegations of kickbacks to the Construction, Forestry, Mining and Energy Union (CFMEU) officeholders and union leaders using standover tactics to force companies to use particular labour hire firms.

But Labor leader Bill Shorten is insisting a police taskforce is the answer and will announce today his support for a joint investigation into allegations of corruption and "low lifes" in the building industry.

"Unlike police, royal commissions do not have the power to arrest, charge or prosecute,'' Mr Shorten said.

"Along with all Australians, Labor condemns corruption and bribery in all its forms, which is why these allegations must be investigated now."

Federal cabinet will finalise the royal commission's terms of reference tomorrow; the deadline for its report is expected to be within 12 months.

Taxpayers can expect a significant bill for the probe: The cost is likely to run as high as $100 million and involve scores of lawyers and hearings.

The investigation also threatens to expose Labor MPs who used union cash to bankroll election campaigns, particularly if it was not properly declared to authorities.

Labor declared $6 million in political donations from unions last year, including $600,000 from the CFMEU, which has been the subject of recent kickback claims.

In supporting a joint investigation, Mr Shorten said: "Anyone involved in corruption - whether they're from a union or not - is a low-life …

"Some of these allegations are sickening and, if they're true, the perpetrators should be locked up.''

Last year Mr Abbott promised an inquiry into allegations of AWU slush funds, allegations that haunted Julia Gillard's prime ministership because of her association with AWU leader Bruce Wilson, a former boyfriend. Ms Gillard denies any knowledge of Mr Wilson's alleged activities, which Victoria Police is investigating.