Two of the largest unions in the AFL-CIO are expected to withdraw from the labor federation today in one of the largest shakeups in the history of the American labor movement. The move comes as the AFL-CIO is marking its 50th anniversary at a major convention in Chicago. Over the weekend, four unions announced they would boycott the convention to protest the direction of the federation. Later today, two of these unions — the Teamsters and the Service Employees International Union — are expected to announce they are leaving the federation altogether. Two other unions — United Food and Commercial Workers and UNITE HERE — are also on the verge of leaving. These four dissident unions represent nearly one-third of the AFL-CIO’s 13 million members. They have launched a new organization called the Change to Win Coalition. Anna Burger, chairman of the new coalition said Sunday “Our differences have become unresolvable. Today will be remembered as a rebirth of union strength in America.” The dissident unions had long criticized AFL-CIO President John Sweeney for not investing enough in grassroots organizing. However backers of Sweeney have warned that the dissident labor groups are playing into the hands of opponents of organized labor. Sweeney said, “Common sense tells us that a union movement divided against itself risks losing the fight for workers’ rights.”