The names of environmental activists have been discovered on a blacklist of thousands of construction workers, it has been revealed.
The GMB union called on a Commons Select Committee conducting an inquiry into the blacklist, which contains more than 3,200 names, to try to find out why the activists were included.
The existence of the list, which was drawn up by the Consulting Association, was revealed after a raid by the Information Commissioner's Office in 2009, which led to the association being closed down.
MPs on the Scottish Affairs Committee have launched an inquiry into blacklisting, which was thought to have only involved construction workers.
But the GMB, which last month published a regional map showing where people on the blacklist lived, said it had been contacted by five female environmental activists who revealed that their names had been included.
The women are from Edinburgh, Leeds, Cornwall, Essex and the North East, and said they had no idea why their names were on the list.
The GMB also revealed that around 240 women were on the list, with no information on whether they were linked to the building industry. The women were from areas including Manchester, London, Birmingham, Cheltenham, Newcastle-upon-Tyne, Sheffield, Bristol, Liverpool and North Wales.
Maria Ludkin, the GMB's legal officer, said the union had never received a satisfactory explanation from construction firms over what they discussed with the Consulting Association. "Now we find environmental campaigners on the blacklist. We are asking the Scottish Affairs Select Committee to investigate how these names got on the list."
Unions claimed workers' names were included if they had raised health and safety issues, or were union activists, and it denied them future employment.
The map published by the GMB, to help identify the 3,200 names, shows the number of workers on the list ranged from just one in Warwickshire, the Isle of Wight, East Lothian, Northern Ireland, Bath and the Orkney Islands, to 454 in London, 183 in Greater Manchester and 173 in Merseyside.