The GMB union was contacted by campaigners who are not in the industry and have no idea why their identities were on the document containing more than 3200 names.
The House of Commons Scottish Affairs Committee has launched an inquiry into blacklisting.
The GMB, which last month published a map showing where people on the blacklist lived, said it had been contacted by the five.
Maria Ludkin, the GMB's legal officer, said the union had not had a satisfactory explanation from construction firms over what they discussed with the Consulting Association. She said: "We are asking the Scottish Affairs Select Committee to investigate how these names got on the list."