One of the world’s biggest web publishing platforms – used by a large chunk of the internet – is locked in a spat which is affecting thousands of businesses worldwide.

While most of the work WordPress does is not seen by internet users, it says its behind-the-scenes web-building tools power 40% of the world’s websites.

That means its disagreement with a company called WP Engine is causing disruption to the huge number businesses that rely on the two organisations to keep their websites running.

Tricia Fox, who runs an agency that manages about 70 websites – and is caught up in the row – told the BBC: “I can’t run a business on this level of uncertainty.”

The very wide use of WordPress makes it “crucial to the internet”, according to Daniel Card, fellow of BCS, the Chartered Institute for IT.

But that also means “its actions definitely have a big ripple effect online”, he says – a ripple effect firms like Tricia Fox’s are starting to really feel.

The row between the companies begins with the fact that WordPress has two sides: its non-profit organisation, called WordPress.org, and its profit-making arm, called Automattic.

WordPress.org makes its source code open, which mean anyone can use it to create and redistribute their own tools for free.

That’s what WP Engine does to run a web hosting service.

But in return for the source code, WordPress expects those who use it to contribute to its maintenance, for example by fixing bugs and testing new features.

The boss of WordPress accuses WP Engine of failing to do so, going so far as to call it “a cancer to WordPress.”

As a result, in late September, he banned WP Engine from using key parts of WordPress.

WP Engine rejects these claims.

“We are proud of our extensive contributions to the WordPress ecosystem,” WP Engine wrote in a post on X/Twitter.

Caught in the middle of this row are the countless websites and blogs that rely on the two companies services.

People like Tricia Fox, who uses a WP Engine subsidiary to host the websites her company serves.

She now says she is “almost certain” to migrate her websites to a different host – a decision which she says is worth “tens of thousands of pounds” over the next few years.

She wants to move away from WP Engine because the fallout has resulted in dozens of hours of extra work for her staff – increasing costs for her business.

“The team don’t know if it’s going to work today or not,” Ms Fox told the BBC.

But she worries even a costly move away from WP Engine may not solve her problems, as she would still be using another host based on the WordPress code.

“What’s to stop WordPress from doing this again [to another company]?” she asks.

“Right now we are currently focused on resolving our dispute with WP Engine,” WordPress said when the BBC asked if it would go after other companies in a similar manner.

The row also underscores how important the open source principle is to the online economy.

While big tech might attract the headlines, for many people and businesses it is something much less eye-catching that keeps them afloat.

“Open source is all about sharing code and standards so everyone benefits, and it’s a huge part of what makes the internet work,” says Daniel Card.

And with WordPress being such a big player in that world, if it makes changes to its tools, he adds, “it’s felt by users everywhere and often impacts hosting, plugins, and web standards across the internet.”

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.

The trademarks do not cover the “WP” abbreviation, but the WordPress Foundation says: “please don’t use it in a way that confuses people”.

WP Engine has meanwhile filed 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 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”.