An investigation has found that British police or security forces supplied personal information to major construction companies looking to keep roughly 3,200 “left-wing or troublesome” workers off their payrolls. The blacklist provided records of “workers’ trade union activities and conduct at work” to more than 40 building firms, The Guardian reports.

David Clancy of the Information Commissioner’s Office—the agency responsible for the inquiry—said the relationship between the group that collected the information and the police and security forces dates back to a time when the government cooperated with building companies to keep an eye on Irish construction workers who may have been involved in IRA terrorism.

John McDonnell, the MP who rang the bell on blacklisting a decade ago and is driving debate on the scandal, fumed: