Billionaire brothers David and Charles Koch have gained fame for assembling a secretive network of wealthy political donors and funneling millions of dollars into our elections through “dark money” non-profit groups and super PACs. The Koch empire is set to spend $300 million on the 2014 election, about as much as George W. Bush and John Kerry each spent on their 2004 presidential campaigns 10 years ago.

By early September, a full two months before Election Day, Koch-funded groups already had paid for nearly 44,000 ads in U.S. Senate battleground races. That’s nearly 1 out of every 10 TV ads aired in those states. This essentially means that TV viewers in Iowa, Kentucky, North Carolina, Kansas, and other Senate battleground states have a 10% chance of seeing a Koch-funded ad during every commercial break. And that’s just TV! These numbers don’t include radio, print, or online advertising. This type of reach is unprecedented in American politics.

Massive  spending on election advertising is  just one way the Koch brothers are seeking to influence U.S. elections. There’s disturbing new evidence that they’re also behind an effort to send targeted voter groups incorrect or misleading voting information through their flagship political organization, Americans for Prosperity (AFP).

AFP’s North Carolina chapter recently sent incorrect voter registration information to thousands of North Carolina voters, and, oddly – at least one cat. The mailing triggered an investigation by the North Carolina State Board of Elections.

North Carolina is home to one of the most competitive Senate races in the nation this cycle, as incumbent Kay Hagen (D) faces state House Speaker Thom Tillis (R). The Koch family has maxed out on direct  contributions to Tillis, and the Koch’s’ AFP and Freedom Partners have spent millions on ads in the race. In fact, outside spending in the North Carolina Senate race now exceeds $42 million, more than in any other contest.

And North Carolina isn’t the only state in which  Americans for Prosperity has used the mail to misinform voters. According to the Institute for Southern Studies, similar mailers with incorrect or confusing voting information also have been distributed in Wisconsin, West Virginia, and Virginia by Americans for Prosperity in recent years.

“It’s outrageous what they do,” said Larry Haake, an election administrator in Chesterfield County, Virginia. “Most of their information is wrong. They know it’s wrong and they don’t care.” In West Virginia’s May primary this year, AFP sent out voter registration leaflets in eight counties that West Virginia Secretary of State Natalie Tennant called “misleading and confusing.”  In Wisconsin, evidence suggests that AFP previously worked with the state Republican Party to send confusing information to minority and student voters.

In North Carolina, AFP argued that the mailers contained just “a few administration errors,” ignoring the fact that the state Board of Elections reported receiving at least 2,000 calls and complaints about them. In West Virginia, AFP’s state director admitted that the mailers may have contained “a few mistakes.” It is unclear if any AFP chapter has sent corrected information to the voters who received their misleading mailers.

The Kochs and Americans for Prosperity have a long record of such stunts. True the Vote, a group known for its voter intimidation tactics, has co-sponsored events with AFP. And both AFP and Koch Industries are members and funders of the American Legislative Exchange Council (ALEC), a group of state legislators and businesses which has pushed “Voter ID” bills that work to depress voting by young people, minorities, and the elderly..

These voter suppression tactics, along with the millions the Kochs are pouring into our elections, represent a major threat to an open and free democracy.