The suit stems from a public feud over WordPress trademark usage and open-source licensing.

WP Engine, which hosts over 200,000 websites, accuses Mullenweg and Automattic of "abuse of power, extortion, and greed." The conflict escalated after Mullenweg called WP Engine a "cancer to WordPress" on his blog, prompting a cease-and-desist letter.

Automattic subsequently demanded eight per cent of WP Engine's monthly revenue as royalties for alleged trademark infringement.

The lawsuit includes 11 complaints, ranging from slander to Computer Fraud and Abuse Act violations.

Mullenweg criticised the company—which has been commercialising the open-source WordPress project since 2010—for profiteering without giving much back and for disabling key features that make WordPress such a powerful platform.

Speaking at WordCamp US 2024, a WordPress-focused conference held in Portland, Oregon, Mullenweg pulled no punches in his criticism of WP Engine. Taking to the stage, Mullenweg read out a post he had just published to his personal blog, where he points to the distinct "five for the future" investment pledges made by Automattic and WP Engine to contribute resources to support the sustained growth of WordPress. Automattic contributes 3,900 hours per week, and WP Engine contributes just 40 hours.

While he acknowledged that these figures are just a "proxy" and might not be perfectly accurate, Mullenweg said that this disparity in contributions is notable, as both Automattic and WP Engine "are roughly the same size, with revenue in the ballpark of half a billion [dollars]."

Mullenweg published a follow-up blog post, calling WP Engine a "cancer" for WordPress. "It's important to remember that unchecked, cancer will spread," he wrote. "WP Engine is setting a poor standard that others may look at and think is ok to replicate."