Matt Mullenweg, co-founder of WordPress and CEO of Automattic announced on Reddit that WP Engine initiated legal action against WordPress, Automattic, and Mullenweg himself. Mullenweg wrote that WordPress is countersuing.
WP Engine is a leading managed WordPress host provider that Mullenweg alleges is violating the WordPress trademark.
But they didn’t use the WordPress trademark to brand themselves. They used “WP”, which WordPress has dedicated to the public domain.