The legislation would impose a minimum 50% turnout in ballots, require unions to provide more notice of future strike action alongside detailed information of the plans, and would change rules on how subs are collected.
Len McCluskey told the audience in Brighton: “Laws are made by governments who are driven by prejudice…
“It is a fact that there are occasions when you have to challenge the law. I have said repeatedly to this Government and the last Government: don’t push us outside the law… because if you do, then the consequences will be your responsibility.”
He called for a “coalition” of dissenting voices to come together to oppose the Bill, including critics on the Conservative benches such as David Davis, the Police Federation and the CIPD, which represents HR professionals, among others.
Addressing the issue of raising voting thresholds, Mr McCluskey, said he supported the concept, but criticised the Government’s method.
While the union chief admitted that it was necessary to do improve turnout, he suggested bringing in modern methods of balloting to achieve this.
Shadow Business Secretary Angela Eagle also gave her view on the challenge of increasing engagement and winning new members, saying it was vital to explain to the next generation why unions were important.
She told the audience: “The benefits that trade unions bring are better industrial relations not worse, more effective and efficient social partnerships at work leading in the best cases to more productive, happier workforces, and more profitable companies.”
Pledging to oppose the Trade Union Bill Ms Eagle described it as a “divisive, partisan, pernicious and vindictive piece of legislation,” which was about “keeping power in the hands of the few.”
Referring to the controversial proposal that would see striking workers on picket lines wearing armbands, Ms Eagle joked: “I don’t know if they want us to tattoo something on our foreheads as well.”
“It is designed to starve the Labour party of money,” she added.
Professor of Public Law at King’s College London, Keith Ewing echoed these concerns over changes to the funding links between the unions and the Labour party.
He said: “Whatever happens the number of people paying the levy is going to decline dramatically. The amount of money that is going to be raised by trade unions for the Labour party is going to fall significantly, and that money is going to have to be made up to support the activities of the party particularly at election times…
“The very nature of the relationship between the party and the unions is at stake as a result of this bill.”
Fellow panel member John Hendy QC, a barrister specialising in employment, human rights and health and safety, described the legislation as an attack on collective bargaining.
He said: “ The basic structure in this Bill is to undermine the right to strike and as we all know… without an effective right to strike collective bargaining is reduced to collective begging.”
Mr Hendy added that the UK’s trade unions laws were already “some of the most restrictive in the western world.”
“That’s the state of the law against trade unions at this time, on which this Bill builds, and that is why it is so serious,” he warned.
Bringing proceedings to a close, Mr McCluskey called on opponents to “stand together to defeat a law that is wrong.”
He concluded: “If this Government doesn’t take a step back then our movement… needs to come together to kick this law out and to make certain that no government of the rich is going to take away our heritage and our ability to represent our members.”