Ad wars among outside interest groups have begun in several U.S. congressional races — about a year before Election Day.

Television spots underwritten a coalition of labor groups urge Montana Rep. Denny Rehberg, Nevada Sen. Dean Heller and Massachusetts Sen. Scott Brown, all Republicans, to protect Medicare, while the Chamber of Commerce launched an ad critical of Democratic Sens. Sherrod Brown in Ohio and Jon Tester in Montana for their stances on several issues, Politico reported Wednesday.

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