New York Attorney General Letitia James said Tuesday that a state-level antitrust investigation into the social network now has the backing of a bipartisan group of 47 attorneys general.
The Democrat and a handful of states launched the probe last month.
It focuses on whether Facebook's dominance is stifling competition, limiting choice for consumers and costing advertisers more money.
James says the group also worries about Facebook's handling of customer data. That drew scrutiny after firms were able to harvest information in attempts to influence the 2016 presidential election.
An email seeking comment was sent to Facebook representatives.
Facebook and other tech giants have also been feeling the heat from federal regulators. The Federal Trade Commission recently fined Facebook $5 billion for privacy violations.