USW has significant membership in the paper making and packaging industries, and many of the companies employing USW members also have UK businesses employing Unite members.

Unite is the UK's biggest union with members working in print, paper making, packaging and the media.

The marriage to USW, the largest private sector union in the US, will lead to a new union called Workers Uniting, which will include members from Britain, Ireland, the USA, Canada and the Caribbean.

One of the core aims of the new union is to synchronise collective bargaining in companies with operations on both sides of the Atlantic.

"This agreement will enable us to use our considerable resources to organise workers from new and growing sectors at home and in developing counties," said Tony Woodley, joint general secretary of Unite.

"There will be no more no-go areas for trade unions."

According to Unite, the tie-up is a response to the challenges of globalisation and, in particular, the growth of casual employment and downward wage pressure affecting workers in Europe and North America.

The new body will also have significant political clout. Unite is the Labour Party's biggest affiliate and donor and the USW is a major contributor to, and supporter of, the Democrats in America and the New Democrats in Canada.