They are now calling on Unite officials to produce any evidence they have on the “unsubstantiated” claims.
The union said: “Unite believes that Crossrail has failed to look at the evidence of blacklisting on the project and has called on Transport for London to investigate possible blacklisting.”
Andrew Wolstenholme, Crossrail Chief Executive said: “Crossrail Limited is not aware of, and has seen no evidence of, blacklisting of any kind in connection with the Crossrail project.
“If Unite has any evidence then we wish to see it; we have made this point a number of times and yet none has been forthcoming.
“Crossrail has written to the trades unions on several occasions setting out our commitment to taking firm, decisive and immediate action if any substantive evidence can be presented.
“All contractors working on the Crossrail project must comply with the Employment Relations Act 1999 (Blacklists) Regulations 2010 which explicitly outlaws the blacklisting of construction workers.
“All our contractors are fully aware that blacklisting is unlawful as well as being a breach of contract which would result in immediate action by Crossrail.”
The Consulting Association was closed down in 2009 following enforcement action by the Information Commissioner – well before the award of the first Crossrial tunnelling and station contracts in December 2010.
Crossrail said it has asked for and received assurances from all its principal contractors providing confirmation that none have engaged in any blacklisting activity on the project.