Union activists have demanded action against a murky "blacklisting" website, which purports to show employers whether their potential employees are union representatives.
Transport union RMT, led by Bob Crow, said information on many of their members, including photos and employment information, is listed on the website HR Blacklist.
The website itself has little information about its owners or where it is based, with only an email form given as a contact option, but it appears to show a number of employees from various professions based in the UK.
An RMT spokesman told The Huffington Post UK that the site was run by "Human Resources Consulting" and was probably based in the US. However The Huffington Post UK has been unable to verify any links between the website and a company with that name.
HR Blacklist has not responded to a request for comment from The Huffington Post UK, with emails to one of the addresses listed all bouncing back.
Numerous RMT activists and other union organisers are listed on the site, including General Secretary Bob Crow and Assistant General Secretary Steve Hedley.
Although a search of the names on the database is free, the detailed files are password protected and only open to subscribers.
According to the RMT, names are listed on the site database without any agreement, in clear violation of data protection.
A union spokesman told The Huffington Post UK that they would be seeking urgent action against the site to protect members, and had asked for advice from the Information Commissioner, which implements the UK's Data Protection Act.
The ICO told The Huffington Post UK they were aware of the allegations and would look into whether the website iwas an offence under their jurisdiction.
Crow said in a statement: "This HR Blacklist website is openly touted on-line and is an extension of the union blacklisting activities of the Consulting Association.
"It lists people as union organisers with the obvious intent of thereby denying them future employment and that is a scandal.
"RMT is taking further advice to protect our members and activists.
“Action should be taken by the authorities to shut this blacklisting site down."
"The site encourages 'HR Agents' to upload and evaluate CVs for the blacklist each time a user pays to access a CV of a blacklisted individual that they have uploaded. The logo calls the site "an ethical human resources community".
He said the site has echoes of the days of the Consulting Association, which held a secret blacklist of 3,200 construction workers who were active union members.
Four years ago, the Information Commissioner's Office found a database, run by the secretive Consulting Association, who had contacts like Balfour Beatty, Costain and Skanska Construction, who used the blacklist to identify potential troublemakers - with information on their families, their attendance at union meetings and demonstrations.
Crow continued: "The whole murky saga of union blacklisting, and the collusion with the police and the security services by the employers organisations, has clear parallels with the Leveson investigations and RMT will continue to campaign with the anti-blacklisting organisations for action against all those involved in this conspiracy."