In that letter, obtained this morning by The Hill, the lawmakers questioned whether data aggregated by advertisers and other third-party sites remains on those companies' servers "indefinitely."
The four lawmakers also asked Facebook to make changes to a new feature that they believe "obligates users to make publicly available certain parts of their profile that were previously private." They also pressed the company to address whether a user's personal information could become public if one of his or her friends does not opt out of the program.
Moreover, they described the entire opting out process as "complicated and confusing to navigate," and they repeated their calls that Facebook change this to an opt-in system.
"We hope that Facebook will stand by its goal of creating open and transparent communities by working to ensure that its policies protect the sensitive personal biographical data of its users and provide them with full control over their personal information," the lawmakers wrote.
"We look forward to the FTC examining this issue, but in the meantime we believe Facebook can take swift and productive steps to alleviate the concerns of its users," they continued. "Providing opt-in mechanisms for information sharing instead of expecting users to go through long and complicated opt-out processes is a critical step towards maintaining clarity and transparency."
Soon after receiving the lawmakers' letter, Elliot Schrage, Facebook's vice president of Global Communications, Marketing and Public Policy, offered a reply, stressing "our highest priority is to keep and build the trust of the more than 400 million people who use our service."
"We look forward to meeting with your staff soon to explain how the collective changes we announced last week will result in more control for users, not less," he wrote. "We also look forward to answering any questions and alleviating any concerns you or your colleagues may have."
"We welcome a continued dialogue with you and others because we agree that scrutiny over the handling of personal data is needed as Internet users seek a more social and interactive experience," Schrage continued. "Facebook is a leader in transparency of our policies, notification to our users, and security of their data."