Senators are targeting Uber after the company said that 57 million accounts belonging to drivers and customers had been breached by hackers.

Why it matters: It's just the latest regulatory headache for Uber, which still has an IPO in its sights.

Democratic Sen. Mark Warner said in a letter to the company's CEO that "Uber's conduct raises serious questions about the company's compliance with relevant state and federal regulations." Warner has been a key critic of the tech industry of late, especially over allegations Russian operatives used online platforms to interfere with the 2016 election.

Sen. John Thune, the chamber's third-highest ranking Republican and the chair of the Commerce Committee, joined three others on a separate letter saying that it was a "a serious incident that merits further scrutiny" and that a payment to the hackers was especially "troubling." That letter also includes Orrin Hatch, the top Republican on the Senate Finance Committee. Both letters request responses from the company.