The union is claiming “substantial compensation and damages” for “destroying workers’ reputations and job prospects”.
Claims were lodged in the High Court in London today by law firm Leigh Day who are acting on behalf of the union.
The claims include defamation related to the damage to workers’ reputations from being on the blacklist.
This is the first High Court case taken by a trade union against all the players in this conspiracy and there will be further cases added to the 70.
Maria Ludkin, GMB National Officer for Legal and Corporate Affairs, said: “GMB is pleased to be the first union to bring this wide ranging High Court action on behalf of our members.
“Finally construction companies will be called to account for their systematic campaign to wipe out union organization on construction sites.
“This is only the tip of the iceberg. There are nearly 3,000 other workers with claims.”