The Guardian's industrial editor, Mark Milner, reports in today's paper that the two are hoping to announce some sort of agreement on the issue this summer.

If so, it would be the culmination of several years of co-operation between the USW and Unite (along with its component parts, Amicus and the Transport and General Workers Union). The two have also been discussing merger for at least the past year or so.

Unite's joint general secretary Derek Simpson argues that merger makes sense as a response to employers' multinational operations. "National unions have dealt with national companies. To deal with international companies you need international unions," as he puts it.

Simpson recognises, of course, that things are a bit more complicated than that. But what sort of issues would a multinational union have to address? Here are some questions Unite and the USW really need to answer before they go ahead.

Would members with opposing interests unite? Since one of the stated aims of a merger would be to counter attempts by multinational employers to move jobs from one country to another with lower wage costs, success would rely on workers in the potential beneficiary country putting the interests of higher-paid UK and US workers first. Is this realistic? Much the same argument could be made in domestic terms – for example when unions oppose relocation from the South East to lower-cost parts of the UK. However, the challenge could be rather greater internationally.

Is there an industrial logic to a merger? In other words, do the two organisations organise in the same or in complementary areas so that a single union would have more muscle? Neither Amicus nor the TGWU had a history of organising in the UK's steel industry, where the USW began life. But both Unite and the United Steel Workers have gobbled up unions in the same sectors – for example, print. Since most print shops are small employers and few operate on an international scale, this may not provide a great example the benefits of an international trade union. Are there more convincing examples?

Is there a legal basis for an international trade union? Almost certainly not, and a single union would probably have to comply with the domestic laws of both the US and the UK (not to mention the laws of other countries in which they wanted to organise). The United Steel Workers has some experience of this as it operates in Canada and a number of Carribean countries, though UK union experience is limited to some operations in Ireland and, in the case of the TGWU, a quirky offshoot in Gibralter. These are largely unchartered waters, and getting it right could be somewhat challenging. How, for example, could an international union comply with UK requirements on leadership elections?

Would an international union do anything an international union federation cannot? There have been international trade union bodies for decades, some of them operating really quite successfully, both as lobbyists within the structures of the European Union and elsewhere, and industrially. The International Transport Workers Federation, for example, has been going since the 1890s and represents union interests in the International Labor Organization, International Maritime Organization and International Civil Aviation Organization. What would be gained by a USW/Unite merger?

However, the USW/Unite courtship is not the only current example of international trade union co-operation. We reported last year on the support given by trade unionists internationally to Italian workers who took their pay dispute with IBM in Italy into the virtual world of Second Life. That co-operation is providing the basis for a more permanent union presence in Second Life, as the launch of SLUnions shows.

There is even the possibility that Unite and the USW may be beaten to the altar by what used to be called the National Union of Marine, Aviation and Shipping Transport Officers (NUMAST).

The union renamed itself Nautilus UK last year and already works closely with the Dutch-based Nautilus NL. The two are planning to tie the knot in May 2009 to create a single Nautilus union. No doubt officials and lawyers at the rather more massive Unite will be studying their progress with some interest.