After the exit of Twitter’s privacy and compliance officers, the Federal Trade Commission (FTC) has said that new chief executive Elon Musk is "not above the law".
The lack of staff in key roles increases the risk of Twitter violating regulatory orders.
The firm was fined $150m in May for selling users' data to help sell targeted ads.
Twitter agreed to new privacy rules and a strengthened security and privacy regime, which was to be implemented by the departed executives.
"We are tracking recent developments at Twitter with deep concern," FTC's director of public affairs Douglas Farrar said.
"No chief executive or company is above the law, and companies must follow our consent decrees."
Farrer said the FTC had "new tools to ensure compliance, and we are prepared to use them".
Elon Musk also told remaining staff that bankruptcy is not out of the question for Twitter, as the layoff of thousands of employees continues.