A Koch brothers group is being investigated for sending mailers with incorrect information about how to register to vote to hundreds of North Carolina voters—and one cat.

Joshua Lawson, a spokesman for the state board of elections, said his office opened the probe Monday after receiving a formal sworn complaint from the state Democratic Party about the mailers, which were sent recently by Americans for Prosperity (AFP). Lawson said state law requires the board to open an investigation if it receives a sworn complaint.

In the complaint, Casey Mann, the state Democratic Party’s executive director, accused AFP of an “attempt to utilize misleading, incorrect, and confusing voter registration mailers as a means of discouraging or intimidating voters in the 2014 general election.”

Deliberately misleading people about how to vote is a felony.

Lawson said that as part of its investigation, the board had already been in contact with lawyers for AFP, and has urged the group to disseminate correct registration information in order to undo the damage.

AFP has said the mailers were an honest mistake, not an effort to mislead voters. But this isn’t the first time that the group, which came to prominence as part of the tea party movement, has sent out inaccurate voting information. And it’s also been involved in organized efforts to make voting harder.

The “official application form” sent by AFP tells people to return their application to the secretary of state’s office, but the envelope is addressed to the state board of elections. In fact, applications shouldn’t go to either place — they should be sent to a voter’s local election board. The form also tells applicants that it’s due 30 days before an election, when it’s actually due 25 days before. And it includes the wrong zip code for the board of elections.

The faulty mailing was first reported Thursday by the Raleigh News and Observer, which also noted several other errors. The state elections board has received hundreds of complaint calls from angry and confused North Carolinians who received the mailer, a spokesman told the paper. One woman said she received a form addressed to her cat.

In a statement, a spokesman for AFP downplayed the mistakes as “a few minor administrative errors.”

Deliberately misleading or not, it’s happened before. In 2011, AFP sent out absentee ballot applications for eight Wisconsin state Senate recall elections, telling recipients to return them by August 11. Problem was, six of the elections were scheduled for August 9. AFP blamed that episode on the printing company it worked with.

AFP is also alleged to have played an active role in helping Republicans suppress the vote. According to a report by One Wisconsin Now, a liberal group, in 2010, AFP discussed a “voter caging” scheme with the Wisconsin GOP and tea party activists, in which a mailer was to be sent to minority and student voters, telling them they had to confirm their voter registration. Any mailers returned as undeliverable were then to be used by tea party volunteers to challenge the eligibility of voters at the polls.

AFP’s Wisconsin director said at the time the effort aimed to combat voter fraud. It’s not clear how much of it was put into practice.

AFP also has hosted events featuring speakers from True the Vote, a tea party-linked group which aims to stoke concern over voter fraud in an effort to build support for voting restrictions. It also has promoted Anita MonCrief, a former Association of Community Organizations for Reform Now (ACORN) employee who now warns about the threat of fraud. AFP bills MonCrief as “the ACORN Whistleblower.”

Nor is the error-strewn North Carolina mailer the only misleading message put out by Tar Heel State conservatives ahead of a tight U.S. Senate race that could help determine control of the chamber. State Senate President Phil Berger recently ran a TV ad which implied, falsely, that voters will be required to show ID at the polls this year. In fact, the ID requirement that was part of the sweeping voting law passed last year by state Republicans doesn’t kick in until 2016. Berger changed the ad after the NAACP filed a formal complaint.

The battle over voting in North Carolina has been steadily heating up since the Obama campaign used a massive minority turnout to win the previously-red state in 2008, and it came close to doing so again in 2012. The Senate race could well hinge on black turnout.

As for AFP itself, there’s an irony here. ACORN was hounded out of existence thanks largely to sloppy procedures in its voter registration drives, which let some employees turn in registration forms that had fraudulent information. AFP and its allies seized on those mistakes to allege massive voter fraud, with essentially no evidence to support the charge.

Even assuming Americans for Prosperity is guilty only of honest mistakes, it may have a similar sloppiness problem to ACORN. After all, it’s happened more than once. But don’t hold your breath waiting for “election integrity” advocates to demand action.

This post has been updated.