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This isn't the first time Franken has sent Uber such a letter. Franken first formally contacted Uber (as well as Lyft, in a separate letter) in November, asking a series of questions about how the car-hailing companies handle consumer privacy.
In December, Uber responded to Franken's original letter, saying the company would improve its privacy policies - but the senator said he wasn't pleased with the response.
"While I'm pleased that I received a reply, I was - and still am - concerned about the lack of detail in the response," Franken said in his second letter.
Franken is calling for added clarification of Uber's privacy policies. He wants to know how many Uber employees have access to Uber's "God View" program - an internal tool that lets employees track the exact locations of customers and riders in real time - and why Uber's employees need access to God View at all.
Back in November, Uber came under scrutiny when the company's top New York City executive, Josh Mohrer, was investigated for breaching Uber's privacy policy by tracking a journalist without her permission. He was later "disciplined," according to the company, and kept his job. Mohrer used a tool called "God View" to track BuzzFeed reporter Johana Bhuiyan's location without asking her for permission, an action that violates the company's privacy policy.
In September, a venture capitalist named Peter Sims wrote a post on Medium called "Can We Trust Uber?" Sims says three years ago, he was taking an Uber SUV through Manhattan when an acquaintance texted and asked whether he was in an Uber vehicle at 33th and 5th. He confirmed that he was, and the acquaintance later revealed she was at an Uber Chicago launch, and at the party Uber had a screen showing where certain people in New York were riding around in Uber vehicles, presumably using the God View tool.
Franken asked in the new letter whether customers have any control over how their data is shared, and what business needs the company has to keep customer data after customers cancel their accounts.
"I remain interested in understanding what, in your view, constitutes a legitimate 'business need' after a cancelled account is fully settled," Franken said in the letter.