WordPress hosting service WP Engine on Monday sent a cease-and-desist letter to Automattic after Automattic’s CEO Matt Mullenweg called WP Engine a “cancer to WordPress” last week.

The notice asks Automattic and Mullenweg to retract their comments and stop making statements against the company.

Today WP Engine sent what is called a “cease and desist” letter to Automattic demanding that Automattic and its CEO Matt Mullenweg stop making and retract false, harmful and disparaging statements against WP Engine. In response to misinformation he has disseminated about the…

— WP Engine (@wpengine) September 23, 2024

WP Engine, which (like Automattic) commercializes the open source WordPress project, also accused Mullenweg of threatening WP Engine before the WordCamp summit held last week.

“Automattic’s CEO Matthew Mullenweg threatened that if WP Engine did not agree to pay Automattic — his for-profit entity — a very large sum of money before his September 20th keynote address at the WordCamp US Convention, he was going to embark on a self-described ‘scorched earth nuclear approach’ toward WP Engine within the WordPress community and beyond,” the letter read.

“When his outrageous financial demands were not met, Mr. Mullenweg carried out his threats by making repeated false claims disparaging WP Engine to its employees, its customers, and the world,” the letter added.

The letter goes on to allege that Automattic last week started asking WP Engine to pay it “a significant percentage of its gross revenues — tens of millions of dollars in fact — on an ongoing basis” for a license to use trademarks like “WordPress.”

WP Engine defended its use of the “WordPress” trademark under fair use laws and said it was consistent with the platform’s guidelines. The letter also has screenshots of Mullenweg’s text messages to WP Engine’s CEO and board members that appear to state that Mullenweg would make the case to ban WP Engine from WordPress community events in his talk at WordCamp if the company did not accede to Automattic’s demands.

Automattic did not immediately respond to a request for comment.

Mullenweg, who co-created WordPress, last week criticized WP Engine for raking in profits without giving much back to the open source project, while also disabling key features that make WordPress such a powerful platform in the first place.

Last week, in a blog post, Mullenweg said WP Engine was contributing 47 hours per week to the “Five for the Future” investment pledge to contribute resources toward the sustained growth of WordPress. Comparatively, he said Automattic was contributing 3,786 hours per week. He acknowledged that while these figures are just a “proxy,” there is a large gap in contribution despite both companies being a similar size and generating around a half billion dollars in revenue. (WP Engine pushes back against that characterization in its C&D letter.)

In a separate blog post, he also said WP Engine gives customers a “cheap knock-off” version of WordPress.

Notably, Automattic invested in WP Engine in 2011, when the company raised $1.2 million in funding. Since then, WP Engine has raised over $300 million in equity, the bulk of which came from a $250 million investment from private equity firm Silver Lake in 2018.