In a landmark decision, Britain’s Competition and Markets Authority (CMA) has ordered Meta Platforms Inc., the parent company of Facebook, to sell its $315 million acquisition of GIF search engine Giphy. This ruling marks a significant shift in global antitrust enforcement, as it’s the first time a major tech company has been compelled to unwind a completed acquisition rather than pay a fine.

The CMA’s investigation found that the merger, finalized last year, would diminish competition between social media platforms, particularly in the display advertising market. Meta now faces two options: to appeal the decision or to proceed with divesting Giphy, a process that would involve finding an approved buyer, subject to regulator vetting.

This order highlights the growing scrutiny of Big Tech companies’ mergers and acquisitions. While global regulators in the U.S. and Europe have previously allowed such deals, often without challenging them, this case represents a shift towards more aggressive antitrust enforcement. Meta’s acquisition of Giphy raised concerns from the outset, with regulators arguing that it would prevent other social media platforms from using Giphy’s popular GIF service, thus strengthening Facebook’s already dominant position.

The decision marks the culmination of a lengthy investigation that began with a probe into how Meta planned to integrate Giphy into its platform. The CMA had previously fined Meta $68 million for failing to update regulators about its efforts to keep Giphy separate before obtaining U.K. approval.

Meta has expressed its disagreement with the ruling, stating that it is reviewing its options, including the possibility of an appeal. The company argues that the decision fails to recognize the benefits of the acquisition and its potential to improve user experience.

In contrast, some global regulators have not raised concerns about the deal. The European Commission, led by Margrethe Vestager, did not review the acquisition, while Austria’s competition agency is still assessing it.

This decision highlights the increasing pressure on Big Tech to prove that their acquisitions do not harm competition, as regulators worldwide begin to take a more scrutinizing approach to their market dominance.