Building workers have been threatened with $10,000 fines for rallying in Brisbane in support of union boss Michael Ravbar ahead of his appearance at a royal commission.
Several hundred unionists showed their solidarity for Mr Ravbar, the Construction, Forestry, Mining and Energy Union's Queensland and Northern Territory secretary, by chairing him into Brisbane Magistrates Court.
But the federal Fair Work Building and Construction (FWBC) agency has warned that they could face penalties of up to $10,200 if construction sites were shut down for the rally, as the royal commission into unions enters its third day in Brisbane.
The agency's director Nigel Hadgkiss said workers who took part in a rally without permission cannot be paid, or ask to be paid, for their time at the rally.
"Their conduct may also constitute unprotected industrial action, which is illegal," he said.
"(We) will not hesitate to bring people before the court where necessary."
Employers or unions can also be penalised up to $51,000 for being involved in paying or demanding strike pay.
Master Builders Australia echoed the FWBC's sentiments on Twitter: "Are these employees on leave? On strike? RDO?"
The FWBC statement was issued as royal commission witness Ian Busch, the Queensland construction manager of Hindmarsh Construction, admitted to the CFMEU's legal counsel John Agius, under cross examination, that he may not have provided all emails to the inquiry.
He was asked if he had conspired with the FWBC in April to sack CFMEU delegate Zoran Bogunovic from an inner Brisbane site during a 12-day industrial stoppage.
"This was all part of a plan to inflame industrial relations," Mr Agius said.
But Mr Busch said he did not recall having discussions with the FWBC about Mr Bogunovic's position.
The CFMEU's national secretary Dave Noonan said the royal commission was biased against unions.
"In this royal commission, there are two classes of witness: business class and economy class," he told AAP on the sidelines.
Mr Ravbar is due to be questioned at the royal commission on Wednesday afternoon.
On Monday, Universal Cranes boss Albert Smith accused the CFMEU of intimidating his business and encouraging clients to boycott his company until he gave in to union demands on enterprise bargaining and a multimillion-dollar redundancy scheme.
Mr Ravbar told the construction workers that the royal commission was a witch hunt against the union movement.
"I plan to go to the court and provide a balanced view of what the trade union movement is all about, to highlight that there is no criminality and corruption," he said.
The inquiry headed by retired High Court judge Dyson Heydon continues.
By Stephen Johnson