A union leader has described the blacklisting of construction workers as a "national scandal" after a study showed the regions most affected by the issue.
Len McCluskey, general secretary of Unite, welcomed Wednesday's Commons debate on blacklisting initiated by Labour, and said there should be a Leveson-style inquiry into the scandal.
Legal action is being taken on behalf of a number of construction workers, who are seeking compensation for having their names on the blacklist.
Labour will call for an investigation into allegations that firms involved in major projects, including the Olympics and Crossrail, blacklisted workers. It said secret files on thousands of workers in the construction sector resulted in them being denied employment after raising legitimate concerns or exercising their human right to belong to a trade union.
Unions have said that more than 40 of the UK's largest construction firms used a blacklist. Many workers have no idea they were included on the blacklist, which was uncovered by the Information Commissioner's Office (ICO) in a raid in 2009.
Mr McCluskey said: "This is a scandal on the scale of phone hacking, except it is the lives of thousands of ordinary construction workers which have been ruined. There should be a full and proper inquiry. Companies have been allowed to get away with a conspiracy to spy on thousands of ordinary construction workers and destroy their careers.
"Lives have been ruined and families have been torn apart just because workers have raised safety concerns in Britain's most dangerous industry or just because they exercised their human rights to belong to a trade union."
Guney, Clark & Ryan confirmed it was taking legal action on behalf of 80 construction workers. Meanwhile, an analysis of the blacklist showed that most workers on the list were from London (454), followed by Greater Manchester (183), Merseyside (173), Glasgow (140), Kent (95), Birmingham (69), Tyne and Wear (69) and North Ayrshire (67).
Employment Relations Minister Jo Swinson said: "The Government condemns blacklisting as a totally unacceptable practice. Legislation has been in place since 2010 to prohibit the use of blacklists following an investigation into the Consulting Association by the Information Commissioner's Office (ICO).
"We would strongly urge anyone who feels they have been a victim of blacklisting, or has any information suggesting that this practice is still occurring, to pass any evidence they have to the ICO."