Four major unions decided Sunday to boycott the AFL-CIO convention, setting the stage for one or more to bolt from the 50-year-old federation in a battle over how to reverse organized labor's decades-long decline, The Associated Press has learned.

The unions, representing about one-third of the AFL-CIO's 13 million members, planned to announce the decision Sunday afternoon, a day before the convention opens, according to three labor officials familiar with the failed negotiations to avoid the walkout.

None of the four dissident unions planned to formally severe ties from the AFL-CIO on Sunday, officials said, but they are now poised to do so at a later date.

The protest is led by Andy Stern, president of the federation's largest union, the 1.8 million-member Service Employees International Union. He is virtually certain to pull his union out of the AFL-CIO in coming days, with hopes of bringing his allies along, officials said.

Joining him in the boycott will be the Teamsters, United Food and Commercial Workers and UNITE HERE, a group of textile and hotel workers, according to the labor officials.

The four unions already had formed the Change to Win Coalition to pressure AFL-CIO President John Sweeney to undertake major changes to the federation.