The social-networking site says the data collection is inadvertent.
"Facebook provides people with control over their information and our focus is on innovating new ways for people to share what they want with whom they want," a Facebook spokesman said in an email. "Facebook does not track people across the Internet, create profiles of their browsing behavior, and sell that information or use it to target ads. There are companies that do and we agree that more should be done to educate consumers about those practices."
Leibowitz also hinted that the FTC is taking a hard look at "supercookies," tracking files that are more difficult to delete than traditional "cookies."
The chairman described supercookies as a "whack-a-mole problem" because they can keep popping up to track users online ever after repeated attempts to delete them.
"Without regard to the specifics, at a general level I think that is in some tension with the approach the Commission wants to take and any responsible company wants to take," he said.
Barton and Markey, who co-chair the Congressional Bipartisan Privacy Caucus, have also called the FTC to investigate supercookies. Barton has said they should be illegal.
Leibowitz made the remarks at a discussion on online privacy hosted by the American Civil Liberties Union and consumer groups.
In his prepared remarks, he urged companies to adopt a "Do Not Track" policy to allow users to control what information they share. He warned that if companies do not adopt the policy voluntarily, Congress could impose Do Not Track requirements.
Leibowitz did not take a position on the Do Not Track legislation that is currently pending in Congress.
—This post was updated at 3:04 p.m.