According to Unite's assistant general secretary Tony Burke, the move is the first step in coordinating collective bargaining and will give the unions additional powers when dealing with multinational companies.

Despite its steelwork title, one of the United Steelworkers' largest industries is the paper and packaging sector.

The two organisations held talks in London last week, and a merger has been endorsed by the executive of Unite. It will go to the United Steelworkers annual conference in July when the two parties hope to finalise the "virtual" merger.

Combined, the two unions would represent around 3m employees in Britain, Ireland, USA, Canada and the Caribbean.

According to the two organisations, this merger would represent much closer workings than the international alliances that have existed between unions in the past. Eventually a single umbrella organisation will sit above the two unions.

The move comes just a year after Amicus joined forces with the Transport and General Workers' Union to form Unite – now the UK's largest trade union.

Commenting on the move, Burke said: "Unite and the USW are similar in structure and in the industries both unions cover. USW has over 120,000 members in papermaking and packaging – many of them in the same companies as Unite.

"The merger is a natural fit for us. Relationships in the paper/packaging sector are well developed and there is already a great deal of cooperation at senior level.

"Last year, a meeting of officials and lay union reps from the USW and Unite in the papermaking and packaging industry took place in the UK and, as expected, the lay reps felt there was no reason why we shouldn't go ahead and create a global union with the USW."