09/29/2010 07:07 am ET Updated May 25, 2011

Baucus Urges Probe Of Advocacy Groups

The Senate's chief tax writer has called for a federal investigation into advocacy groups that have become increasingly popular vehicles for outside donations.

These groups, known as 501(c)4s after the section of the tax code that defines them, can raise unlimited donations from individuals, corporations and labor unions to spend on political advertisements.

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