Corruption whistleblowers from the construction industry need a forum to be heard, Treasurer Joe Hockey says, in support of an inquiry into alleged union misconduct.
Amid mounting claims of improper deals by union officials, including some with bikie gang members, Mr Hockey said the actions of the movement "need to be fully exposed and addressed".
"Someone has to stand up for the workers and we're prepared to do that," he told ABC TV on Wednesday.
Stopping short of backing a royal commission into the matter, Mr Hockey said an inquiry need not extend to all employer groups.
"There are no suggestions of other representative groups engaging in this, what appears to be, systemic corruption," he said.
While singling out the union movement for investigation, Mr Hockey said some of the representative bodies continued to work for their members.
"Good union representatives and the good unions would be appalled at the revelations that now seem to be flowing out from a range of different sources."
Mr Hockey said the federal government would still have a productivity inquiry into industrial relations reform as promised to business but other priorities had taken precedence.