Thousands of construction workers across Australia risk having their pay docked when they down tools in support of the CFMEU.
Rallies are planned for the nation's capital cities on Tuesday after Attorney-General Mark Dreyfus placed the union into administration following allegations of links to organised crime and corruption.
In a statement, a spokesperson for the Fair Work Ombudsman said if an employee failed to go to work or walked off the job without permission, this could be a contravention of workplace laws.
"Where an employee has engaged in unprotected industrial action, the employer is required under the (Fair Work) Act to deduct a minimum of four hours wages from the employee, even if the industrial action was less than four hours," it said.
The CFMEU flagged it would launch a legal challenge of the take over, saying members were denied due process and democratic rights.
Attorney-General Mark Dreyfus placed the CFMEU into administration. (Lukas Coch/AAP PHOTOS)
The Electrical Trades Union and maritime union backed the protest and urged their members to join rallies, describing the administration an "attack on trade unionists' rights".
In a social media post, the ETU slammed the treatment of the union in comparison to companies which weren't placed into administration following royal commissions into banking and aged care.
"The CFMEU on the other hand - one of Australia's strongest unions, is now forced straight into administration on the back of a handful of rumours and allegations," the post reads.
"The hypocrisy is staggering!!"
A spokesperson for the CFMEU administrator said "the taking of unprotected industrial action is not lawful".
"The CFMEU is no longer involved in organising any protest tomorrow," they said.
More than 200 CFMEU officials were terminated after the attorney-general placed its construction and general divisions into administration, alongside all of its state and territory branches.
Any union property possessed by officials such as cars, mobile phones, laptops and documents could be taken.
The administration period could last up to five years and officials found guilty of crimes would be banned for life and unable to become bargaining agents at other registered organisations without holding a fit-and-proper-person certificate.
Ex-CFMEU NSW secretary Darren Greenfield and his son Michael, a former union leader, will have their cases return to court in NSW over corruption charges.
The pair, who are on bail, are accused of accepting bribes from a building company for preferential treatment from the union and access to contracts.