The senators, in a letter to FEC Chairwoman Caroline Hunter, pointed to loopholes in disclosure rules, Politico reported. Under current law, for example, while political action committees must disclose their donors, they can include contributions from non-profit 501(c)(4) groups that do not have to disclose contributors.
"While the First Amendment guarantees the right of free speech, we must be sure that the corporate structure does not obscure the speaker," the senators wrote. "This is why we believe that the identity of individual contributors should also be disclosed when they make substantial donations to organizations financing independent expenditures."
The signers included 10 Democrats -- Jeanne Shaheen of New Hampshire, Al Franken, Minnesota, Jeff Merkley, Oregon, Tom Udall, New Mexico, Sherrod Brown, Ohio, Michael Bennet, Colorado, Chuck Schumer, New York, Sheldon Whitehouse, Rhode Island, Barbara Boxer, California. and Kirsten Gillibrand, New York-- and Vermont Independent Bernie Sanders.
2014: The Year in Music [PHOTOS]