Recent revelations about Facebook’s use of cookies may attract the attention of the Federal Trade Commission. Meanwhile Spotify has launched a “private listening mode” in response to complaints about its integration with Facebook.

We noted on Tuesday that Australian blogger Nik Cubrilovic had uncovered the fact that Facebook was continuing to use personally identifiable tracking cookies even after user’s had explicitly logged out of the site. Facebook says the cookies are necessary but that it deletes them immediately after use and it was working on making them anonymous (which it now appears to have done.)

Now two politicians, Republican Joe Barton and Democrat Ed Markey, have raised the issue with the FTC. In a letter to its chairman Jon Leibowitz they say “When users log out of Facebook, they are under the expectation that Facebook is no longer monitoring their activities. We believe this impression should be the reality.”

According to the politicians, the FTC has the authority to investigate this issue as it may constitute “unfair and deceptive acts or practices.”

In another response to Facebook privacy concerns, Spotify’s CEO Daniel Ek has said “We’re rolling out a new client as we speak where you can temporarily hide your guilty pleasures. It works like a browsers private mode.”

The new setting, found under the application’s “File” menu, is clearly related to two recent revelations: that Facebook now claims the right to post information from third-party applications about a user’s behavior without explicit permission; and that Spotify is demanding that new users have a Facebook account before signing up.