Plans to create a so-called 'super union' have suffered a setback with GMB members voting against the merger.
The T&G and Amicus had hoped to merge with the GMB from January 2007, creating a labour group of about two million members.
It is thought the decision made at the GMB’s conference in Blackpool was partly motivated by fears that its regional structure would suffer.
The T&G and Amicus said they would go ahead with a merger and expressed disappointment at the decision.
In a joint statement they said: “The T&G and Amicus will now proceed with our planned creation of a new union to meet the great challenges facing people in the 21st century, a democratic and campaigning union which will fight back for employees in the workplace, will take trade unionism out to the millions of unorganised workers, will stand up for equality for all.
"Such a union will, we believe, rapidly become attractive to other unions in this country, and will build ever-stronger links with trade unions around the world."