The Federal Trade Commission (FTC) and the Department of Justice say Twitter violated an agreement it had with regulators, court documents showed.
Twitter had vowed to not give personal information like phone numbers and email addresses to advertisers.
Federal investigators say the social media company broke those rules.
Twitter was fined £400,000 in December 2020 for breaking Europe's GDPR data privacy rules.
The FTC is an independent agency of the US government whose mission is the enforcement of anti-trust law and the promotion of consumer protection.