The Construction Industry Joint Council has agreed to insert an anti-blacklisting clause into its agreement.
The Council covers 500,000 construction workers.
The new clause, inserted into the CIJC Working Rule Agreement, says the body “does not condone any form of blacklisting of any worker.”
UCATT said it had led a union movement to write in the rule.
Steve Murphy, general secretary of UCATT, who proposed the new clause, said: “This is a major step forward, blacklisting is a vile and disgusting practice. There must be no hiding place for blacklisters in construction or any other industry.”
Mr Murphy added: “The majority of the major companies responsible for blacklisting follow the CIJC agreement. By inserting this clause we are a further step forward in eradicating blacklisting from our industry for once and for all.”