Balfour Beatty will today face the Employment Tribunal in London accused of dismissing a blacklisted worker.
Mick Dooley, who ran for election as Ucatt general secretary last year, claims Balfour Beatty let him go from a site in Victoria in 1993 because of information held about him on the blacklist.
He is claiming £35,000 from the construction giant, plus further damages.
It is the first claim following an investigation by the Information Commissioners Office which uncovered a database that had been set up to allow contractors to vet workers.
A total of 14 firms were issued with enforcement notices by the ICO for subscribing to the Consulting Association database, while blacklist owner Ian Kerr was fined £5,000.
The blacklist provided private information about more than 3, 000 construction workers to contractors.