• by Wendy Davis  @wendyndavis, December 9, 2011

Four members of the U.S. House of Representatives sent a letter to Facebook CEO Mark Zuckerberg this week pressing him for more details about the company's privacy practices.

“With great opportunity comes great responsibility, and with more than 800 million active users and an untold number of nonusers visiting Facebook or partnering Web sites every day, your company has the opportunity to collect vast amounts of data about an enormous number of people,” says the letter, signed by Rep. Cliff Stearns (R-Fla.), Diana DeGette (D-Colo.), Joe Barton (R-Texas) and Ed Markey (D-Mass.).

The lawmakers specifically ask Zuckerberg to address recent reports that it tracks people who visit sites with the “like” button -- regardless of whether those people are logged into Facebook at the time, or even have profiles with the service.

“What browsing or tracking information does Facebook collect for both users and non-users?” the lawmakers ask. “Can users or non-users opt-out of this information collection? If so, how?” the letter continues.

The Congress members also question Zuckerberg about some aspects of Timeline -- a new addition to users' profiles that makes older posts more accessible to others. Users will have five days after receiving Timeline to hide data before it's published to their profiles. People can still delete material after Timeline is published, but that might be too late to prevent some users from being embarrassed.

The lawmakers question how Facebook arrived at five days, and whether that's long enough for users. “How do you respond to concerns that it will be onerous for users to carefully review each post and photo in just five days, particularly for longtime or highly active users?” they ask.

A Facebook spokesperson said: "We look forward to reviewing the letter from Chairman Stearns and Ranking Member DeGette, and we are pleased to answer any questions they may have." Separately, Markey and Barton criticized Facebook for refusing to take part in a Dec. 14 briefing about the privacy of children and teens.

“Given Facebook’s widespread use by children and teenagers, as well as its recent settlement with the Federal Trade Commission over privacy violations, we felt that it was important for Facebook to participate in this briefing,” the lawmakers said in a letter to Zuckerberg.

Facebook recently agreed to settle a Federal Trade Commission complaint by promising to obtain users' opt-in consent before sharing their information with a wider audience than users' expected when they posted the material. A Facebook spokesperson said the company “is committed to continuing to offer easily accessible tools so people can control how they share information and with whom.”

He added: “We communicate regularly with lawmakers about these issues and look forward to continuing that productive dialogue."