The surveillance and blacklisting of thousands of workers, including some suspected by construction companies of being left-wing troublemakers, should be immediately investigated by the privacy watchdog, it was urged last night.

More than 40 major firms referred to the secret database, which listed thousands of people's details, including their involvement in union activity, before hiring staff. Workers who were on the list allege they were deprived of their livelihoods as a result of their inclusion, with supporters claiming their human rights have been breached.

Liberty has written to the Information Commissioner, Sir Christopher Graham, accusing him of inaction over a privacy scandal that it compares to phone hacking. Liberty is threatening to go to court to force him to investigate the case.

Details of the blacklist emerged in 2008 when it emerged that an organisation called Consulting Association held files on about 3,200 agency workers, including political activists, shop stewards and health and safety representatives. Some of the information was gathered using secret surveillance.

The database was seized three years ago and Ian Kerr, who had operated it, was fined £5,000. Invoices were discovered showing that 44 companies had paid to see the names on the list.

But full details of the material it contained only emerged as workers began to pursue legal action over their inclusion.

An official from the Information Commissioner's Office (ICO) told the industrial tribunal of a person who had been blacklisted that he believed the information on the database could only have been supplied by the police or the security services.

Meanwhile, Sir Robert McAlpine, the construction giant and builder of the Olympic stadium, has been served with legal papers over its alleged involvement in the database. In light of the legal action, Liberty said the time had come for the ICO to reopen an investigation into the use of the blacklist.

Corinna Ferguson, legal officer for Liberty, said: "We can't believe the inaction of the Information Commissioner on a human-rights violation of such wide public interest.

"Contracting out the blacklisting of innocent workers, politicians and journalists is no better than farming out phone hacking to private detectives and the consequences for our democracy are just as grave. If we cannot persuade the Commissioner to discharge his public duty, we will consider seeking assistance from the courts."

The Information Commissioner's Office said it had received Liberty's letter and would respond in due course. A spokesman said: "In 2009 the ICO closed down the construction industry's blacklist operated by the Consulting Association. Ian Kerr, who ran The Consulting Association, was prosecuted and fined £5,000 and a number of construction companies were served with enforcement notices. These were the highest powers we had available to us at that time. Our action was widely welcomed."

A spokesman for Sir Robert McAlpine said: "As legal proceedings have been issued, it would be inappropriate for Sir Robert McAlpine Ltd to make any comment at this stage."