Demonstrations were today being held outside the Wolverhampton headquarters of the construction giant Carillion.
moreIt comes amid a union day of action which was held against alleged blacklisting.
Around 15 representatives of the GMB union and the Birmingham Trades Council waved flags and placards outside the firm's Birch Street offices.
Blacklisting came to light in 2009 after a raid by the Information Commissioner's Office unearthed a secret list of 3,213 workers targeted for being union activists.
In October, eight construction companies, including Carillion, announced they were developing a scheme to compensate workers on the list, but the demonstrators say it is not enough.
Carillion spokeswoman Jane Smith said: "Carillion has made it very clear that we do not condone or engage in blacklisting and we pride ourselves on our values and high standards of corporate governance."