Public school teachers in Ohio recently got some surprising news in the mail: They were due a “credit” from their union.

Melissa Cropper, president of the 20,000-member Ohio Federation of Teachers, was listed as the sender of the “CREDIT DUE NOTICE.” All educators had to do was fill out the attached form and mail it back for an apparent refund.

There was just one problem. The notice didn’t actually come from Cropper or the union ― it came from the Freedom Foundation, a conservative group whose mission is to get teachers and other public sector workers to drop their union membership.

Anyone who carefully read the form would see that by signing it, a teacher would be authorizing the Freedom Foundation to submit it to their union and employer on their behalf to renounce their membership.

“People are really pissed,” said Randi Weingarten, president of the American Federation of Teachers, the Ohio union’s parent group.

Weingarten said she is accustomed to the foundation ― which has ties to GOP megadonors ― “misrepresenting” teachers unions and their work. But she believes the group crossed a legal line this time by listing Cropper as the sender of the document.

“They lie all the time, and their MO is to divide and divide and divide,” she said. “This one was a complete fraud.”

A teacher who quits their union would stop paying dues out of future paychecks. But the mailer didn’t just imply that teachers were owed a credit, Weingarten said ― it also suggested the union’s own leader “is inducing you to drop the union.”

The Freedom Foundation declined to answer detailed questions about the mailer campaign, such as how many were sent out and how many the group received back from teachers. But Ashley Varner, a spokesperson for the group, defended the use of the mailers in an emailed statement to HuffPost.

“Freedom Foundation informs public employees, including teachers, of their constitutional right to leave their unions and stop paying dues because unions like AFT fail to do so,” Varner said. “The communication with teachers in Ohio was neither fraudulent nor misleading. Randi Weingarten’s claims are simply untrue.”

Nonetheless, the Freedom Foundation backed down from using the mailers after receiving a cease-and-desist letter from the AFT, according to letters provided to HuffPost. The foundation agreed not to send any more mailers, and assured the AFT that it hadn’t distributed any outside of Ohio.

The union’s general counsel, Dan McNeil, said in a letter to the foundation that its “reliance on trickery and deception to further its insidious goals is not only morally repugnant, it is also unlawful.” McNeil alleged that the effort ran afoul of both trademark law and identity fraud statutes, and that it amounted to “federal mail fraud.”

Freedom Foundation executive vice president Brian Minnich wrote in a response that the group “respectfully disagrees” that the letter was meant to deceive teachers. Although the letter’s sender was listed as the union president, Minnich said the return envelope and tear-off form “clearly indicated the return would go to the Foundation.”

The mailers are part of a long-running conservative effort to weaken public sector labor groups that tend to support Democrats. Republicans in states around the country have taken aim at teachers unions in particular, pushing laws designed to make it harder for the groups to hang on to members and influence education policy.

This right-wing cause got a major lift from the Supreme Court in 2018.

The conservative majority ruled in its landmark case Janus v. AFSCME that public sector workers could not be required to pay any dues to a union, even if the union is still legally obligated to represent them. The decision effectively made the entire U.S. public sector “right to work,” and forced public sector labor groups to change the way they operate and focus more on member retention.

After the ruling in Janus, the Freedom Foundation started pouring resources into campaigns encouraging workers to drop their unions. The recent Ohio mailers were part of a project called “Opt Out Today.”

It’s difficult to unpack how the Janus decision has affected teachers unions nationally so far, in part because membership hinges on school staffing levels that fluctuate. The Freedom Foundation claims teachers have been opting out of AFT “in droves,” but Weingarten says this doomsday scenario has not come to pass.

“They used Janus to try to defund unions. What’s happened in terms of our union is, it hasn’t worked,” she said. “But the amount of time, energy and effort we have to spend correcting the record and dealing with these misrepresentations and out-and-out lies, that takes time away from us servicing the members.”

Weingarten said the Freedom Foundation’s use of the “credit due” mailer is a sign of “desperation.” She noted that in the group’s Oct. 12 response to the union’s cease-and-desist letter, the group said that it had “not forwarded a single request to opt-out received recently” from the Ohio mailer campaign.

The union demanded a list of all members who received the mailers, but it says the Freedom Foundation hasn’t provided one yet. The union suggested in a follow-up letter that it might pursue legal action.

“The AFT reserves all rights,” the letter read.