Organisers hope the consolidation will strengthen trade unions in countries where their existence is weak or under threat while promoting more effective measures against practices of multinational companies considered harmful to workers.

One of the world's largest trade union movements, the World Confederation of Labor (WCL), dissolved itself on Tuesday and is to be regrouped under the new body.

A second organisation, the International Confederation of Free Trade Unions (ICFTU), was expected to take similar action.

Tother, the WCL and ICFTU represent more than 180 million workers worldwide.

The new ITUC, which will be formed on Wednesday at the start of a three-day congress in the Austrian capital, will also incorporate a dozen national trade unions without any international affiliation, such as the French CGT or the Argentinian CTA.

The giant will ultimately embrace 190 million unionists worldwide.

Staying away from the ITUC however will be the the Communist-affiliated World Federation of Trade Unions (WFTU), which after the WCL and ICFTU is the third largest trade union group in the world.

With 145 syndicates and 42 million workers, the WFTU said it was defending "a class line" and criticised the ICFTU for making "compromises and concessions."

But ICTFU general-secretary Guy Rider, who is expected to head the new organisation, said its creation was a "historic" event after decades of strife among trade unions.

"(The ITUC will) build world trade union strategies to counter those (strategies) of capitalism," he said, adding that globalisation had led "over twenty years to a major fall in revenue, to the detriment of salaries and for the benefit of capital."

The ITUC will have to "confront multinational companies" and "support trade unionism where it is weak and oppressed," Ryder said.

"Trade unionism is weakening under pressure from neo-liberal globalisaton," according to WCL Secretary-General Willy Thys, and is losing ground both in former European strongholds such as Britain and Germany and in the United States where its membership has been halved in 15 years.

Trade unionism is also under threat in Central America, Africa and in parts of Asia.

To strengthen its influence, the ITUC hopes to build closer ties with "civil society" groups, such as non-governmental organisations, and to take part in anti-globalisation forums and organise worldwide mobilisations.

The congress will open on Wednesday with a speech by Austrian President Heinz Fischer before the new confederation adopts its charter.

On Thursday, the director-generals of the World Trade Organization (WTO), Pascal Lamy, and the International Labour Organization (ILO), Juan Somavia, will speak during a day of debates.

The head of the ITUC will be elected on Friday when Ryder gives the closing speech of the congress.