WASHINGTON, Dec 8 (Reuters) - The chair of the U.S. Senate Commerce Committee on Wednesday asked a regulator to investigate whether Meta Platforms" (FB.O) Facebook misled its advertising customers and the public about the reach of its advertisements. In a letter to Federal Trade Commission (FTC) Chair Lina Khan seen by Reuters, Senator Maria Cantwell said "evidence suggests that Facebook may have deceived its advertising customers about its brand safety and advertising metrics" and "may have engaged in deceptive practices." Meta and the FTC did not immediately comment. Cantwell added that "public information suggests that Facebook’s potential misrepresentations about brand safety and advertising metrics may be unfair, as well as deceptive." She said "a thorough investigation by the Commission and other enforcement agencies is paramount, not only because Facebook and its executives may have violated federal law, but because members of the public and businesses are entitled to know the facts regarding Facebook’s conduct." Cantwell cited a 2020 Senate report that Facebook reportedly controlled approximately 74% of the social media market. In October, Senator Richard Blumenthal said both the Securities and Exchange Commission and the FTC should investigate claims made by a Facebook whistleblower that the company knew its apps were harming the mental health of some young users. The FTC has filed an antitrust lawsuit against Facebook that urged a court to demand that the company sell two big subsidiaries. The FTC"s case against Facebook represents one of the biggest challenges the government has brought against a tech company in decades, and is being closely watched as Washington aims to tackle Big Tech"s extensive market power. The FTC originally sued Facebook during the Trump administration, and its complaint was rejected by the court. It filed an amended complaint in August that Facebook has asked be tossed out.