Unite's Len McCluskey at an anti-austerity march/LNP REX Shutterstock

The UK’s biggest union, Unite, has passed a motion to remove a clause in its rules that requires members to remain within the law when staging protests, it has been reported.

Speaking at the union’s conference this weekend, general secretary Len McCluskey said that he would not see his union “rendered toothless by passively submitting to unjust laws”.

He added that the union, which has almost 1.5 million members, was right to question “a commitment to stick, under any and all circumstances, within the law as it stands, and as the Tories are preparing to change it”.

Members approved the removal of the words “so far as may be lawful” from rules governing the union’s actions, effectively clearing the way for unlawful strikes.

The Government, meanwhile, is preparing to rush through its Trades Union Bill, which was announced in May’s Queen’s Speech.

It is thought that the Bill, which imposes minimum turnout thresholds on strike ballots and requires 40% of eligible voters who work for essential services such as fire, health and education to back a strike before it can go ahead, will be introduced this Wednesday.

At present, a strike can go ahead as long as there is a majority, even if turnout is low. Under the new rules, a strike would only be lawful if the ballot attracted at least a 50% turnout.

The legislation will also impose further restrictions on picketing and a repeal of the current rule preventing the use of agency workers to cover for striking employees.

Last week a 24-hour tube strike over pay increases and bonuses for drivers working on a new night-time service caused chaos for employers and commuters in London.

Although McCluskey avoided advocating law breaking in his speech, he said that the union was “ready for the fight”. He added: “We will, I believe, find allies among everyone who cares for freedom and democracy.”

But Tom Kerr Williams, an employment partner at DLA Piper, warned that employees taking part in unlawful strikes could be taking a risk.

He said: “Lawful strikes are protected by ballot and unions have, of late, been wary of taking unlawful action because of the legal implications associated.”

“Where a strike is not protected by a ballot, unions can be liable for damages up to £250,000, which might not cover the total cost of employers, but could have significant financial impact for the unions.”

He added that employees taking part in unlawful strikes could find themselves in breach of contract, and eligible to be fairly dismissed.

“While this announcement is, in part, sabre rattling by Unite, targeted unlawful action can be incredibly disruptive and we could see a return to some ‘carry on at your convenience’ activity with shop stewards calling employees out without warning,” said Kerr Williams.

“Employers need to remain vigilant and remember that they have a number of legal options at their disposal to limit strike activity. Unite’s recent announcement will not change this, and employers should keep their legal options under review if faced with such action.”