Papa John’s is preparing for a fight against John Schnatter, the pizza chain’s founder and former chairman, by adopting a so-called poison pill defense to protect itself against a hostile takeover attempt.

The plan, announced late Sunday by the company’s board, is meant to prevent any shareholder from amassing a controlling interest in Papa John’s. Mr. Schnatter, who resigned as chairman this month after a report that he had used a racial slur in a comment about black people, owns 30 percent of the company’s stock, making him its largest shareholder.

Mr. Schnatter has said since stepping down that doing so “was a mistake” and that he was pressured to leave by board members acting on “rumor and innuendo.”

The poison pill strategy — which has been used by, among others, Avis, Netflix and Sotheby’s, and in a battle between Men’s Wearhouse and Jos. A. Bank — is typically employed to fend off takeover efforts by activist investors and acquisitive rivals. It has rarely been used to preemptively rebuff a company founder, one notable exception being the poison pill that American Apparel adopted in 2014 amid an acrimonious split with its founder, Dov Charney.