The 19-year-old college student aiming to unseat Ald. Marty Quinn (13th) filed a $4 million defamation lawsuit this week against the Chicago Teachers Union that names Quinn and his key political ally, House Speaker Mike Madigan, as potential defendants.

On Monday, DePaul University freshman David Krupa sued the CTU and Chicago Public Schools teacher Jeanine Muir, naming Quinn, Madigan and the vaunted 13th Ward Democratic Organization as respondents in discovery.

The filing marks Krupa’s latest pushback against the 13th Ward’s powerful leadership. In January, he filed a federal civil rights lawsuit that accused Quinn and Madigan of using fraud and intimidation to force him off the ballot.

The latest suit holds that Muir, a teacher at Nathan Hale Elementary School in the 13th Ward, used a CTU letterhead when she penned a note to ward residents accusing Krupa of cyberbullying and cyberstalking.

“Mr. Krupa harassed and bullied me through breaching a school computer system and posting disturbing language and images that shocked me and my student,” Muir wrote in the letter, which implores residents not to vote for Krupa.

“My sense of personal safety and security were violated, and this letter is part of my effort to hold him accountable for his behavior,” she wrote.

Krupa rebuffed Muir’s claims in his lawsuit, calling the letter “false” and “defamatory.”

Krupa and his attorney, Anthony J. Peraica, are seeking $4 million in damages from the CTU and Muir. Peraica, a former Cook County Commissioner, also represents Jason Gonzalez, who filed a suit claiming that Madigan put up sham candidates in the March 2016 primary for his house seat.

CTU spokeswoman Chris Geovanis said Muir reported the situation with Krupa to the school district and was merely looking to protect her students.

“She was satisfied the conduct was terminated,” Geovanis said.

Geovanis held that Muir’s use of a CTU letterhead was appropriate because the letter dealt with “a matter of public information and public interest.”

“The behavior is none-the-less troubling, and a matter of public interest considering this candidate’s already known history of abusive behavior,” added Geovanis, who included a link to a Politico report that details an abuse allegation lodged against Krupa by his former girlfriend.

Krupa’s suit also names Quinn’s wife, Beth, as an employee at Hale, something the alderman scoffed at.

“Naming my wife, who has served the children of Chicago as a dedicated speech pathologist for decades and has no involvement in my campaign, in a baseless lawsuit is a new low for Tony Peraica, the Republican Party and its latest pawn, David Krupa,” Ald. Quinn said in a statement.

“Suing two public school teachers is a new low,” Madigan echoed in his own statement. “Certainly they don’t have the Republican backing to defend themselves like David Krupa does. These outrageous lawsuits are a disservice to the residents of the 13th Ward who are trying to focus on the issues that matter most to them.”

Earlier this year, Krupa filed a federal lawsuit after Quinn withdrew a controversial ballot challenge amid a flurry of fraud accusations.

The suit claims that Quinn supporters submitted thousands of potentially bogus affidavits that were allegedly signed by people seeking to revoke their signatures from Krupa’s nominating petitions. Additionally, Krupa used the suit to accuse Quinn and Madigan of using strong-arm tactics to keep him from running.

At the time, Quinn called the lawsuit “an effort to distract voters from my opponent’s extreme right-wing agenda.”