Unite hopes a global presence will increase its influence
The UK's biggest union Unite is reportedly on the brink of merging with a counterpart in North America.
A deal between Unite and the United Steelworkers' union (USW), is hoped to be sealed by the USW's convention in July, the British union said.
An agreement would be a milestone in organised labour's efforts to deal with the globalisation of business.
The combined group would have more than three million members in the UK, the US, Canada and the Caribbean.
Talks between the union were held last week in London to thrash out the details of the establishment of the first transatlantic union.
A Unite spokesman told Associated Press that the talks were a "first step" and that many details had yet to be finalised.
"We are dealing with global companies that can move capital - and employment - around the world at will in many cases," said Andrew Murray.
"While big business is global and labour is national, we are going to be at a disadvantage."
Although there are different labour laws in other countries, union officials hope that a combined group will increase their bargaining clout in talks with multinational conglomerates.
It is thought the deal will eventually pave the way for the formation of a new umbrella organisation, with a single management structure and leader.
Labour unions from other regions, including from red-hot emerging economies in Asia, Eastern Europe and Latin America, are also being encouraged to co-operate.
Unite represents employees at some of Britain's biggest companies, including defence firm BAE, Rolls-Royce, brewer Scottish & Newcastle and Scotland's only oil refinery, Grangemouth.
The union is the product of last year's merger between the Transport and General Workers Union (T&G) and Amicus.