The UK’s controversial Online Safety Act is facing a legal challenge from the foundation behind the online encyclopedia Wikipedia.

In a blog post by Wikimedia Foundation’s Lead Counsel Phil Bradley-Schmieg, wrote that “8 May, 2025, the Wikimedia Foundation, the non-profit that hosts Wikipedia, announced that it is challenging the lawfulness of the UK’s Online Safety Act (OSA)’s Categorisation Regulations.”

Specifically, the Wikimedia Foundation is seeking a judicial review of the OSA’s ‘Categorisation Regulations’.

The Online Safety Act was passed into law back in October 2023, and implemented stringent measures against social media platforms, search engines, messaging systems, gaming and dating apps and pornography and file-sharing sites for failing to remove illegal content.

Online Safety Act

Ofcom, the UK’s communications regulator, is in charge of enforcing the Online Safety Act.

“We are arguing that they place Wikipedia and its users at unacceptable risk of being subjected to the OSA’s toughest ‘Category 1’ duties, which were originally designed to target some of the UK’s riskiest websites,” wrote Bradley-Schmieg, on behalf of the Wikimedia Foundation.

The Wikimedia Foundation said it shares the UK government’s commitment to promoting online environments where everyone can safely participate.

But it said that if enforced on Wikipedia, Category 1 duties would undermine the privacy and safety of Wikipedia volunteer users, expose the encyclopedia to manipulation and vandalism, and divert essential resources from protecting and improving Wikipedia and the other Wikimedia Projects.

It said that under this category, Wikipedia says it will be required to carry out user verification and filtering duties, which it warns would damage its system of volunteer users and communities who edit and review content on the site.

The foundation said the new duties would mean that while it would not require it to verify the identity of all users, it would be required to allow any user to block other unverified users from editing or removing content they post, upsetting the hierarchy the site currently has in place.

The platform warned this change could mean malicious users could easily post harmful, false and misinformation content, and block Wikipedia’s volunteer editors from then removing it.

Government not listening

And despite years of talking with UK regulators and policymakers, these issues remain unaddressed said Wikimedia.

“The categorisation rules are now in force, and the first categorisation decisions from the UK’s online safety regulator, Ofcom, are expected this summer,” wrote Bradley-Schmieg. “The solutions we proposed – including clarifying the new rules – were not accepted.”

“With time running short, we have initiated a legal challenge to the Categorisation Regulations,” said Bradley-Schmieg. “We are taking action now to protect Wikipedia’s volunteer users, as well as the global accessibility and integrity of free knowledge.”

The Wikimedia Foundation said it is not bringing a general challenge to the OSA as a whole, not even to the existence of the Category 1 duties themselves.

“Our legal challenge will solely focus on broad new categorisation rules that risk imposing Category 1 duties on Wikipedia, either this year or the next, 2026,” said Bradley-Schmieg.

Frankenstein law

The Wikimedia Foundation pointed out that litigation was avoidable – and nothing prevents its quick resolution.

It pointed out that new laws, such as the EU’s Digital Services Act (DSA), are usually written flexibly.

Others, for example in Australia, France, and Germany, can be more specific, but then avoid collateral damage by exempting non-profit organisations or educational projects.

The foundation labelled the Online Safety Act a “Frankenstein” law, which is around 300 pages long, and imposes more duties than any other online safety law.

It also noted that the OSA has even accumulated over 1,500 pages of supplemental Ofcom guidance and Codes of Practice – with more yet to come.

“We regret that circumstances have forced us to seek judicial review of the OSA’s Categorisation Regulations,” wrote Bradley-Schmieg. “Given that the OSA intends to make the UK a safer place to be online, it is particularly unfortunate that we must now defend the privacy and safety of Wikipedia’s volunteer editors from flawed legislation.”

Controversial law

There is no doubt the OSA is controversial, and big name tech firms have consistently voiced their opposition and concerns about the legislation.

In 2023 WhatsApp and Signal for example said they would rather pull out of the UK than comply with the act’s requirements.

But it is now a law, and in April Ofcom had announced its first investigation under the OSA into an online suicide forum, said to be linked to at least 50 deaths in the United Kingdom.

In March, Ofcom had gained the legal powers to take action against websites hosting illegal material, after duties came into force that meant service providers (including large tech platforms) must now implement safeguards to take action against illegal harms.

In January technology secretary Peter Kyle had criticised the Online Safety Act as “very uneven” and “unsatisfactory” on socially harmful content, but stopped short of committing to changes.

Ofcom meanwhile also warned in January that “robust” age verification checks on all websites containing pornography, must be in place by July 2025 at the latest under OSA requirements.