Some workers who raised safety issues were allegedly blacklisted
Several firms accused of subscribing to a secret database of building workers' details have denied any wrongdoing.
The Information Commissioner says a firm called the Consulting Association flagged up workers who had raised safety concerns or who had union links.
Balfour Beatty and Amec said they did not condone "blacklisting". Emcor and Laing O'Rourke denied discriminating against workers on any grounds.
The Department for Business said it would consider outlawing blacklisting.
This would happen if evidence showed it was going on, a spokesman said.
Unions have called on the government to act swiftly to pass anti-blacklisting regulations which were prepared in the 1990s but never introduced.
An investigation by the Information Commissioner's Office (ICO) found that a Droitwich-based company called the Consulting Association had allegedly sold details about workers, including information concerning personal relationships, trade union activity and employment history.
The ICO now plans to prosecute the firm, run by Ian Kerr and now thought to have ceased trading, for a "serious breach" of the Data Protection Act.
It said about 40 construction companies who subscribed to the scheme would send lists of prospective employees to it and in return would be warned about potential troublemakers.
Some of the notes on individuals included descriptions such as "ex-shop steward, definite problems" and "Irish ex-Army, bad egg". Others related to workers who had raised concerns over health and safety issues, such as asbestos removal.
One of the firms listed in the ICO's report, Balfour Beatty, said it "does not condone the use of 'blacklists' in any circumstances".
"We have taken steps to ensure that none of our companies use the services of the Consulting Association," it added.
Another firm, Amec, echoed the denial. "Amec does not operate a policy of 'blacklisting' individuals and the senior management of the company would not condone such a policy," it said.
Morgan Ashurst said it inherited a subscription to the Consulting Association upon acquiring another company.
"An internal investigation into this subscription has shown that we did not supply to, or receive any data from Ian Kerr or the Consulting Association, nor did we use any information from this organisation since the acquisition," a spokesman said.
"Now that the subscription has been brought to our attention, and the person who subscribed to it left the company last year, we have cancelled it."
Laing O'Rourke also said it had "a legacy relationship" with the company born out of an acquisition, which had now "ceased".
A spokesman for another firm named by the ICO, Emcor Group UK, said it was "an equal opportunities employer" whose policy was "not to discriminate on any grounds".
The Consulting Association was unavailable for comment.
Deputy Information Commissioner David Smith said he was deeply disappointed that firms he described as "household names" had been involved in an allegedly illegal system for many years.
He said they would be issued with a legal order not to repeat the offence, and if they breached it they too would face prosecution.
Following the raid on 23 February, investigators discovered that the Consulting Association's database contained the details of some 3,213 workers, the ICO said.
Employers paid £3,000 as an annual fee, and £2.20 for individual details, the ICO said. Invoices to construction firms for up to £7,500 were also seized during the raid.
The TUC and the building workers' union Ucatt called on the government to introduce legislation to make blacklisting illegal.
Alan Ritchie, general secretary of Ucatt, said: "It is the only way to protect the rights of trade union members."
A Department for Business spokesman said: "We have the power to make it illegal to use blacklists.
"We would review whether to use this power if there was compelling evidence that blacklists were being used."
Liberal Democrat home affairs spokesman Chris Huhne said: "Leading companies have to realise that information is power, and wrong information is the abuse of power.
"The Information Commissioner is absolutely right to throw the book at the miscreants in this case."