It is understood the union is seeking compensation for 70 workers.
It states the clients had their job prospects and reputations ruined as a result of the blacklist and are therefore taking legal action on their behalf.
Law firm Leigh Day, which is acting for GMB, is seeking compensation and injunctions for workers kept out of work as "a direct result of an unlawful conspiracy by construction employers". The claims include defamation, given the damage to workers' reputation from being on the blacklist.
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This is the first High Court case taken by a trade union against those implemented in the conspiracy, adding that it was just "the tip of the iceberg", with around a further 3,000 workers also having claims.
The controversy regarding the blacklist was brought to attention in 2009 by the Information Commissioner's Office (ICO). Following a raid, the ICO seized a database of 3,213 names of construction workers and environmental activists used by 44 companies.
The blacklist was drawn up by the Consulting Association, which has since been closed down, and GMB claims that the 70 members it is representing were "blacklisted by Carillion and other construction employers".
However, according to the BBC, a spokesman for the firm said: "Carillion has not received any communication at all from the GMB or its solicitors in respect of any proposed litigation so we are a little surprised at their latest press release.
"Any Carillion involvement with the Consulting Association referencing service ended by 2004. This was long before the practice became unlawful. As you would expect, Carillion will defend itself vigorously in any litigation."
(JP/CD)
