Facebook has to pay more than 50 million pounds (almost 60 million euros) to the British market watchdog Competition and Markets Authority (CMA).
The company has violated imposed rules regarding the investigation into the acquisition of video service GIPHY, the regulator said.
Facebook bought GIPHY in May last year for more than 340 million euros, but the CMA stated that the purchase would harm competition in the online advertising market.
The watchdog instructed Facebook to ensure that GIPHY remained a separate company that would not be further merged with the other services of the social medium.
Facebook also had to report regularly on how it met those requirements.
The CMA now states that Facebook has not provided all the required information in its reports, despite multiple warnings and two lost legal proceedings.
The CMA speaks of a "major violation" and therefore imposes a fine of 50 million pounds.
In addition, Facebook has to pay another £500,000 because it replaced its responsible director twice without asking permission from the CMA.
The British watchdog reports that it has never happened before that a company had to be fined because it did not want to comply with the rules surrounding an investigation into a takeover.
The fine is, according to Joel Bamford, who is responsible for reviewing mergers and acquisitions at the CMA, "a warning to any company that thinks it is above the law".Keywords: competition and markets authority, facebook, rules, british, company, investigation, acquisition, video service, giphy, joel bamford, competition, regulator, watchdog, services, purchase