Facebook's latest privacy policy update has once again gotten the company in hot water, this time with four US senators. Senators Al Franken, Charles Schumer, Michael Bennet, and Mark Begich wrote an open letter to Facebook on Tuesday, urging the company to take "swift and productive steps" to make user information more private and warning that the Federal Trade Commission may get involved if certain concerns aren't addressed soon.

Being questioned is Facebook's decision to categorize a user's hometown, current city, "likes," interests, friends, and other info as "public information." Now, even the most private user cannot have a Facebook account to communicate with friends while also keeping this information hidden from public view, and the senators believe this creates a "potential gold mine of data for unsolicited advertisements."

Schumer, who composed the letter on behalf of the group, said that Facebook should change its policies so that sharing all this information is opt-in instead of opt-out (in some cases, users can't even opt out if they wanted to). "The current policy puts at risk users who are not technically proficient enough to change the settings, or are not aware of the newly changed privacy policy," the group wrote.

Schumer has also asked the FTC to look into privacy disclosures by social networking sites, and to provide guidelines on how these networks can use private information. He added that if the FTC doesn't feel it has the tools or authority to put together these guidelines, he would be "willing to offer legislation."

That seems like a (not-very-veiled) threat towards Facebook and its kin, but Schumer and gang are serious about their concerns. On top of making more information public by default, the senators are also worried that the latest changes would allow third-party advertisers to store user data indefinitely. And it's not as if the FTC doesn't already have Facebook on its radar. Just four months ago, the Electronic Privacy Information Center (EPIC) asked the FTC to investigate Facebook's last controversial changes to its privacy policy.

Facebook maintains that it discusses its privacy program in depth with "many regulators" prior to rolling out changes, but it seems that the public's expectations still aren't quite in line with what Facebook thinks should be public.