Other outside dark money groups get the press, but the U.S. Chamber of Commerce gets results. That's because the Chamber, the biggest lobbying organization in the country, doesn't disclose its donors, among whom are the most powerful companies in the country. Those corporations use the Chamber's to anonymously funnell money into competitive races. In the beginning of October alone, they've spent almost $5 million dollars on political races. But that's not the source of their unmatched influence.