The protesters have called for a public inquiry into the scandal. Others demanded that construction firms who are implicated in the blacklisting of workers should not be awarded government contracts.
The blacklist was drawn up The Consulting Association and it is thought around 600 Scottish construction workers have appeared on it, some of which have lost out on work as a result.
-- Advertisement --
For the list, construction firms paid to access it, but the Association was closed down in 2009 after it was raided by the Information Commissioner's Office.
It is understood some of the companies involved were working on major building projects in Scotland.
Rozanne Foyer, Senior Regional Organiser at Unite, said: "We are here to demand justice for our members who have been blacklisted for decades, whose lives have been ruined, whose families have been put into poverty."
Labour MSP Neil Findlay added that the full extent of the practice would not be known until there was an inquiry.
He explained: "It's a human-rights abuse that has been going on for decades.
"I would like the Scottish government to engage with with the trade unions and others who have got an interest in this issue, and I would personally like the Scottish Parliament to have an inquiry into this to find out the extent in Scotland."
MSPs were debating the issue in parliament.
(JP/CD)
