A group of U.S. senators sent a letter to Uber's CEO on Monday saying the company's recently revealed data breach "merits further scrutiny."

Hackers stole data from 57 million Uber drivers and users, Chief Executive Dara Khosrowshahi revealed on Nov. 21. Uber paid hackers $100,000 to delete the data and keep the breach under wraps, and the company did not report the incident for more than a year.

Khosrowshahi, who was not employed at Uber when the breach occurred in 2016, has offered affected drivers free credit monitoring and identity theft protection. The company also fired Chief Security Officer Joe Sullivan.

Lawmakers said Monday that they need more information on the timeline of the incident and the employees involved.