Blain Dillard complained about the student-driven and group work focused curriculum on his website, blog and on social media.
All the way in Utah, the math company "Mathematics Vision Project" or "MVP" was not happy.
They're now suing Dillard, saying he "commenced a crusade against MVP" with comments they call false and defamatory.
They say his public opinions have also harmed the company financially.
Other parents have had similar opinions and say this lawsuit is trying to scare parents into silence.
Dillard calls the lawsuit intimidation and bullying and infringes on his free speech.
Friends have now set up a GoFundMe page to help him with legal fees.