Union bosses have warned ministers they will take them to court unless they ditch draconian anti-strike legislation.
MPs will vote on Monday on a new law that would ban some public sector workers from joining walkouts.
Paul Nowak, the general secretary of the TUC, accused ministers of "going back to the 1980s" by confronting unions rather than trying to resolve the disputes.
He warned the bill would mean that when workers democratically voted to strike, they could be forced to work and sacked if they did not comply.
"This is a naked power grab that will severely restrict the fundamental right to strike - no matter how ministers try and spin it," he said.
"The Government's own impact assessment says this Bill will poison industrial relations, lengthening disputes and ultimately leading to more frequent industrial action."
Mr Nowak said the legislation would put the government in breach of international law on the right to strike.
"The proposals are likely to be unworkable, so why is the Government wasting time and energy on going back to a 1980s playbook rather than trying to resolve disputes?"
TUC assistant General Secretary Kate Bell said unions were getting ready to go to court to challenge the proposed law.
“We are preparing so that if it does become legislation, we have everything ready so that we can challenge it,” she said.
Ministers have been accused of trying to "rush through" the bill, but union leaders believe it will come under detailed scrutiny in the House of Lords, which could hold it up.
More than 100,000 people have already signed a petition in opposition to the move, while the TUC is holding a series of protests across the country on February 1, the day 100,000 civil servants are due to go on strike in one of many disputes with the Government over pay and staffing.
The Government insists it is "fair and reasonable" to guarantee a minimum level of services during industrial action.
Mr Nowak is calling on Jeremy Hunt to come out of hiding and stump up the cash to end the NHS strikes.
The tight-fisted Chancellor is refusing to provide extra funding so nurses and ambulance workers can get a proper pay rise.
The TUC has accused Mr Hunt of being “missing in action”.
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