The WP Engine web hosting service is suing WordPress co-founder Matt Mullenweg and Automattic for alleged libel and attempted extortion, following a public spat over the WordPress trademark and open-source project. In the federal lawsuit filed on Wednesday, WP Engine accuses both Automattic and its CEO Mullenweg of “abuse of power, extortion, and greed,” and said it seeks to prevent them from inflicting further harm against WP Engine and the WordPress community.

WP Engine is a major rival to WordPress.com, with more than 200,000 websites using the service. Mullenweg runs Automattic, which owns WordPress.com, a company that sells a hosted version of the open-source WordPress software — just like WP Engine.

The lawsuit was initiated after a weeks-long fight over trademark infringement and whether WP Engine should pay licensing fees to use the WordPress project’s open-source software. Mullenweg called WP Engine a “cancer to WordPress” on his blog, with WP Engine then sending a cease-and-desist letter asking for the comments to be withdrawn. Automattic later alleged that WP Engine was infringing on WordPress and WooCommerce trademarks, and demanded eight percent of the company’s monthly revenue as royalty payment.

In its lawsuit, WP Engine lists 11 complaints that accuse Mullenweg and Automattic of libel, slander, attempted extortion, and violating the Computer Fraud and Abuse Act. WP Engine also claims that the WordPress Foundation — the non-profit organization led by Mullenweg that backs the open-source WordPress project — failed to disclose its trademark ownership to the IRS, and accuses Mullenweg of making false statements to the IRS.

“Matt Mullenweg’s conduct over the last ten days has exposed significant conflicts of interest and governance issues that, if left unchecked, threaten to destroy that trust,” WP Engine said in a statement posted to X. “WP Engine has no choice but to pursue these claims to protect its people, agency partners, customers, and the broader WordPress community.”