The billionaire Koch brothers have played a crucial role in U.S. politics by funneling millions of dollars into the fledgling Tea Party movement and right-wing groups. Today, the left-wing magazine Mother Jones offers up what it says is "exclusive audio" from inside the brothers' secret fundraising-and-strategy seminar in June.

The seminar, held at a resort near Vail, Colo., was attended by about 300 wealthy guests, MoJo reports. It writes that the audio "was provided by a source who approached the author after the event was over and was not seeking compensation."

Charles and David Koch co-own the energy-and-chemical conglomerate Koch Industries, the country's second-largest privately held company, which is headquartered in Wichita. They have held the hush-hush seminars twice a year since "at least 2003," the magazine says.

MoJo writes:

These unprecedented recordings provide a behind-the-scenes look at how the Koch brothers and their comrades talk when they gather. They include a pair of keynote speeches and remarks by brothers Charles and David Koch, who spell out their political aims and name some of the "great partners" who have contributed millions of dollars to their causes. ... "There is anonymity that we can protect," noted emcee "Kevin"—likely Kevin Gentry, a VP for the Charles G. Koch Charitable Foundation—as he gently urged guests to open their wallets in support of the brothers' causes. Indeed, Charles Koch named 32 individuals and families who had donated more than $1 million over the previous 12 months, yet because of loopholes in federal campaign law, their donations do not exist in the public record.

The magazine provides a breakdown of the Koches' "million-dollar donor club" and says that on Wednesday, it will report on "the GOP superstar who rocked the Koch seminar crowd."