Trade union Unite is merging with US-based union United Steelworkers to create a trans-Atlantic body called Workers Uniting.
The BBC reported the plan is to synchronise pay talks with multinational companies and the deal will be signed in Las Vegas later.
According to the report, the new organisation will have three million members.
Joint general secretary of Unite Derek Simpson told the BBC: "The political and economic power of multinational companies is formidable.
"They are able to play one nation's workers off against another to maximise profits. With this agreement we can finally begin the process of closing that gap."
Unite is the largest union in the UK, with over two million members in the public and private sectors.
It was formed last year in the merger between Amicus and the Transport and General Workers Union.
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