Building firms and government departments were told to come clean today amid a growing torrent of evidence on large-scale blacklisting.
Labour shadow business secretary Chuka Umunna said there were "very serious questions to answer."
He expressed concern about revelations that information on hundreds of environmental activists had been held in a special file with green-coloured cards.
And construction union Ucatt general secretary Steve Murphy demanded an urgent public inquiry following damning revelations made in hearings before a key committee of MPs.
Alarm mounted following a tricky parliamentary performance by disgraced blacklister Ian Kerr, who was fined £5,000 in 2009 for administering the Consulting Association (CA) database.
A former key operator in the right-wing Economic League, Mr Kerr attempted to play down his own role in the CA and fingered construction firms who set it up in 1993.
An estimated 40 construction firms paid the CA around £2,500 per year each plus around £2 for every blacklisted name, he revealed in evidence to the Scottish Affairs select committee.
Mr Kerr named Robert McAlpine and Balfour Beatty as Olympic site blacklisters and revealed that construction companies had sought information on potential employees for the Crossrail project, PFI hospitals, Wembley Stadium and major government buildings.
He also admitted that cards with information on activists had been colour-coded when cross-questioned on the details by committee chairman Ian Davidson.
Black cards were for construction workers while green cards were for environmental activists and he "thought" that orange cards were for trade workers in mechanical engineering.
He told the committee that he was "trying to remember" what blue cards were for.
Mr Davidson interjected: "I presume it does not refer to Conservative or to Rangers?"
Mr Kerr responded: "I think they were old."
He also admitted that around 200 names of environmental activists and animal rights campaigners were held at the CA.
Mr Davidson said it was "absurd" that a favourable view of the Morning Star had been one of the items recorded on CA personal files.
He had personally seen a seized file in which "it was down against somebody that they said the Morning Star was the only paper that supported the unions."
If you appreciated this article then please consider donating to the Morning Star's Fighting Fund to ensure we can keep developing your paper.
Nothing will bring back the hundreds of British soldiers killed fighting in Iraq at Tony Blair's behest.
Under a modicum of scrutiny the PM's international 'achievements' quickly unravel
The Con-Dems have had it their way too long. We have to turn this country around