The union says it wrote to and contacted directly members of the Joint Committee on Statutory Instruments, expressing “grave concerns” about the proposed law. It says when the committee met on 20 January to consider the regulations, a decision was made to delay ratifying the regulations for a week, as the committee were concerned that the proposals do not comply with human rights obligations.

UCATT general secretary Alan Ritchie said: “The pause in the parliamentary process is welcome. Outlawing blacklisting is a fundamental issue for UCATT. The government now has the opportunity to rethink and redraft regulations which as they stand are entirely inadequate to stamp out blacklisting.”

The union wants the law amended to make blacklisting a criminal offence and for a wider definition of the “trade union activities” falling in the scope of the measures. It also wants workers to be told automatically if their details are discovered to be on an illegal blacklist.

Richard Arthur, head of trade union law at Thompsons said: “Blacklisting is different to other forms of discrimination, because it is by definition, planned, covert and systematic.

“The Employment Relations Act 1999 which provides the enabling legislation, envisaged that there would be criminal sanctions for blacklisting trade unionists. It sends the wrong message to potential law breakers to now say that only civil law sanctions such as fines will apply.”

The Government consultation followed the raid by the Information Commissioners’ Office in March 2009 on the premises of the Consulting Association, run by Ian Kerr. ICO officials found a blacklist containing the names of more than 3,200 construction workers. More than 40 major construction companies were subscribers to the list.

Mr Kerr, who reportedly earned six figure sums for operating the list, was fined just £5,000 at Knutsford Crown Court for breaching the Data Protection Act and paid £1,187 costs. The Consulting Association was largely funded by construction companies – many of them household names – but none has so far not been prosecuted.

Thompsons had warned the Government against waiting until there was evidence of employers using blacklists before implementing the legislation. As predicted, the damage has already been done to the workers on the Consulting Association’s list and to the numerous others blacklisted by employers for such alleged misdemeanours as raising health and safety concerns. Thompsons has had to tell them that there was no law to protect them.

“But under the proposed regulations it will still be difficult to pursue blacklisting discrimination cases,” said Arthur. “The regulations will still require individuals to pursue claims, rather than allowing a trade union to do so on behalf of groups of members. What makes blacklisting so objectionable is the publication of an association between an individual and trade union membership or activities. By requiring individuals to put their name to proceedings this will simply be perpetuated.”

The Government also proposes time limits for taking claims which will make it excessively difficult in practice for claimants to exercise their rights. And while the regulations would make it unlawful to compile a blacklist, they do not provide a right to complain to an employment tribunal over the simple fact that the claimant has had their personal details included on a blacklist.

“This is a serious omission that must be rectified,” Richard Arthur said.

Read the full response by Thompsons Solicitors on The Blacklisting of Trade Unionists: Consultation on the Revised Draft Regulations.