The UK's competition authority the CMA said it will look into whether Facebook has unfairly used the data gained from its advertising and single sign-on to benefit its own services.
Europe has simultaneously launched its own investigation with the CMA saying it will work closely with the European Commission as it carries out its probe.
The US social media giant collects data from its digital advertising services to allow other businesses to advertise to Facebook users and from Facebook Login, which allows users to sign in to other websites, apps and services.
Facebook Marketplace, where users and businesses can put up classified ads to sell items and Facebook Dating, a dating profile service it launched in Europe in 2020 will be especially scrutinised said the regulator.
Andrea Coscelli, chief executive, said: “We intend to thoroughly investigate Facebook’s use of data to assess whether its business practices are giving it an unfair advantage in the online dating and classified ad sectors.
“Any such advantage can make it harder for competing firms to succeed, including new and smaller businesses, and may reduce customer choice.
“We will be working closely with the European Commission as we each investigate these issues.”
No decision has yet been made on whether Facebook has broken the law, the CMA added.