News that the formation of a 'super union' has moved a step closer have been given a cool reception by employers.
Last week the executive committee of the GMB union agreed in principle to start merger negotiations with Amicus and the Transport and General Workers' union (T&G).
Supporters say the super union - which would have about 2.5 million members - would have enough influence to stand up to global businesses and could recruit thousands more workers.
It is anticipated that the new union will devote 20m per year to recruiting new blood - an unprecedented amount in British trade union history.
However, the CBI said it was not the size of the union that matters, but how modern it is.
"Unions that work with companies to enhance productivity and performance have a legitimate role to play," said CBI deputy director general John Cridland.
"But those that use industrial relations language of the past have little relevance in the modern labour market," he added.
David Yeandle, deputy director of employment policy at the EEF manufacturers' organisation, said although any merger meant companies might be exposed to a union with significant resources, it remained to be seen how they would use them.
Stephen Luckhurst, HR director at technology solutions company Qinetiq, said that although a merger would in theory increase the union power base, he was unsure what difference it would make in practice.