Trade union members criticised the fine handed to Kerr
Some of Britain's leading construction firms subscribed to a secret blacklist of workers which prevented them from getting jobs, a court has heard.
More than 40 firms used the database of 3,213 workers - which included details of trade union activity - to vet workers, Knutsford Crown Court heard.
Ian Kerr, 66, of Avoncroft Road, Stoke Heath, Worcestershire, has been fined £5,000 for administering the list.
He pleaded guilty in May to breaching the Data Protection Act.
Knowledge of the list emerged in March when officials from the Information Commissioner's Office (ICO) visited the offices of the Consulting Association, in Droitwich, Worcestershire.
Kerr was one of four employees at the association, which was described in court as a construction trade association.
John Wyn Williams, prosecuting for the ICO, told the hearing on Thursday that the body was funded by construction companies from across the UK.
"It would collate and provide information to construction companies in relation to individuals seeking employment in that industry," said Mr Wyn Williams.
The database included names, dates of birth, national insurance numbers and details of whether an individual had any connection to trade union activity.
It included details of "conduct which may impact on an individual's chances for further employment", he added.
"This information was to be used covertly. Individuals on the database were not aware of it and could not challenge the accuracy of the information," Mr Wyn Williams told the court.
Kerr was jeered by construction workers as he left court
The ICO said it believed Kerr ran the blacklist for up to 15 years. The court heard that accounts showed it was paid £478,000 between 2004 and March 2009.
After the hearing, ICO investigator Dave Clancy said the inquiry would continue to see if the companies involved had broken the law.
"We are looking to see if the requirements of the Data Protection Act have been complied with. We will take action in due course," said Mr Clancy.
George Guy, regional secretary for the construction workers' union Ucatt, said he was disappointed by the result of the hearing.
He said: "The people who provided this information and received it have got off scot free.
"Some of our members were out of work for years because of this list.
"They were forced to live in poverty, unable to provide for their families and they had no idea why.
"We will continue this fight until the companies involved are brought before the courts."
Mike Abbott, 77, from Wigan, Greater Manchester, was named on the list in the late 1970s and said he was only offered two jobs in one five-year period.
"I couldn't feed my children because of that list and all Kerr gets is a £5,000 fine," he said.
"I am very angry about what he did to me and many others. But he was just a front for all this."
David Smith, deputy information commissioner, said: "Ian Kerr colluded with construction firms for many years flouting the Data Protection Act and ignoring people's privacy rights.
"Trading personal details in this way is unlawful and we are determined to stamp out this type of activity."