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.
The officials spoke on condition of anonymity, saying they were not authorized to discuss the decision.
The protest is led by Andy Stern, president of the federation's largest union, the 1.8 million-member Service Employees International Union.
Joining him will be the Teamsters, United Food and Commercial Workers and UNITE HERE, a group of textile and hotel workers, according to the labor officials.
It was unclear which, if any, of the unions would take the next step and leave the AFL-CIO altogether, although CBS News Correspondent Cynthia Bowers reports that Service Employees International is said to be considering a permanent break.
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.
The boycotting unions, which represent mainly service and retail workers, blame the steep decline in union membership on the current AFL-CIO leadership and its failure to deal with the change from an industrial based economy, Bowers reports.
"We have to change, and we believe we need more members if we're going to have an impact on helping working families have what they deserve in America," Teamsters president James P. Hoffa told CBS News.
Three others unions that are part of the dissident coalition had not planned to leave the Chicago convention: the Laborers International Union of North America, the United Brotherhood of Carpenters and Joiners of America, and the United Farm Workers.
Officials said Stern's group probably would sever ties with the AFL-CIO, perhaps as early as Sunday, with hopes of bringing the Teamsters, UFCW and UNITE HERE along.
The other three unions may delay deciding whether to leave the federation, officials said.