Campaigners have condemned strike reforms as a "major attack on civil liberties" after the Government raised the prospect of forcing all picketing workers to give their names to police.
Proposed new laws have gone out to consultation that mean trade unions would have to appoint a picket supervisor and issue them with a letter of authorisation as well as take "reasonable steps" to inform police of their name, contact details and where picketing would take place. The supervisor would also have to wear an armband or badge identifying them.
But the consultation on the Trade Union Bill also raises the possibility of a "requirement for all pickets to be properly identifiable in the same way as the supervisor".
Sara Ogilvie, a policy officer at Liberty, warned that the move would deter workers from picketing and claimed the Government was "playing fast and loose" with its obligations under International Labour Organisation (ILO) standards.
She told The Independent: "With a history of blacklisting, it's entirely understandable why trade union members don't want to identify themselves to the police."
Under the Bill, a turnout of at least 50% of members will be needed to authorise action. In key public services - such as health, education, fire, transport, border security and energy - there will be an additional hurdle that a strike must be endorsed by 40% of those entitled to vote.
The package would also ensure that union members had to actively ''opt in'' to political levies - the proceeds of which are overwhelmingly paid into Labour coffers - and reduce restrictions on firms' use of agency staff.
In the consultation, the Government says it wants to introduce new measures to make picket lines more transparent to stop intimidation of workers.
But campaign groups Liberty, Amnesty International and the British Institute for Human Rights, accused the Government of wanting to undermine workers' rights.
"The Government's plans to significantly restrict trade union rights - set out in the Trade Union Bill - represent a major attack on civil liberties in the UK," they said in a joint statement said.
"By placing more legal hurdles in the way of unions organising strike action, the Trade Union Bill will undermine ordinary people's ability to organise together to protect their jobs, livelihoods and the quality of their working lives."
The statement added: "It is hard to see the aim of this bill as anything but seeking to undermine the rights of all working people. We owe so many of our employment protections to Trade Unions and we join them in opposing this bill."
TUC general secretary Frances O'Grady said: "The Trade Union Bill threatens the basic right to strike - a fundamental British liberty.
"Instead of trying to ram the bill through parliament without proper scrutiny and consultation, ministers need to take a step back, recognise that they were wrong, and drop these proposals.
"The Government's excessive new restrictions on peaceful picketing and protests and unions' use of Facebook and Twitter have no place in a modern democracy.
"Ministers should be working with unions to deliver a fairer Britain, not dreaming up new ways of stopping their members from defending jobs and pay and standing up for decent services and safety at work."
A Department for Business, Innovation and Skills spokesman said: "None of these changes are about banning strikes but we need to get the balance right between the interests of unions and the interests of the majority of people who rely on important public services. These modernising reforms will ensure strikes only happen as a result of a clear, positive decision by those entitled to vote."
Shadow industry minister Stephen Doughty said the Government was taking a "sledgehammer" to workers' rights.
He said: "The concerns being expressed about proposed picketing provisions are very valid.
"The vast majority of industrial action has, and will continue to be, conducted in a peaceful and respectful way.
"This is the Government using a sledgehammer approach to basic rights of association and protest."