While much of the spat between the two sides has taken place through official social media accounts and blog posts, it has also entered the courtroom.
WordPress.org cannot force WP Engine to contribute to its open source project – but it does have control over its trademarks.
It argues that WP Engine mentions WordPress in its marketing tools to help sell its product – and therefore should pay to use the trademark.
“Any business making hundreds of millions of dollars off of an open source project ought to give back, and if they don’t, then they can’t use its trademarks,” Mr Mullenweg wrote in a blog post, external.
The trademarks do not cover the “WP” abbreviation, but the WordPress Foundation, external says: “please don’t use it in a way that confuses people”.
WP Engine has meanwhile filed, external a legal case against Mr Mullenweg and Automattic, with accusations of attempted extortion, libel and a violation of the Computer Fraud and Abuse Act among its complaints.
It claims Automattic told WP Engine they would have to pay “tens of millions of dollars” in order to continue using the WordPress trademarks.
WP Engine has since asked, external for the legal process to be sped up as its businesses are suffering.
Its recent filing claimed the number of cancellation requests it receives have increased by 14% compared to normal trading, as a result of the disruption.
It said it it is also losing out on potential new customers due to uncertainty over its future access to WordPress products.
Automattic has called the lawsuit “baseless” and “flawed, start to finish.”
“We vehemently deny WP Engine’s allegations – which are gross mischaracterizations of reality,” it said in a statement, adding that it would “vigorously litigate against this absurd filing”.