The changes would clarify that Facebook has the right to include users' photos, names and other personal information in advertisements to their friends.
Markey said he is "particularly concerned" about how the changes would affect teens. Facebook said that by agreeing to the new policy, users who are younger than 18 "represent" that their parents have also agreed to the terms.
"Teens, often impressionable and still developing and learning safe online habits, are especially vulnerable," Markey said. "Accordingly, the FTC should pay close attention to any change that could harm our nation's young people."
Markey's letter echoes the concerns of a coalition of privacy groups, who urged the FTC to block the changes last week.
Facebook argues that it is only clarifying its policy statement and not changing any of its actual practices.
"We routinely discuss policy updates with the FTC and this time is no different," a Facebook spokeswoman said. "Importantly, our updated policies do not grant Facebook any additional rights to use consumer information in advertising. Rather, the new policies further clarify and explain our existing practices. We take these issues very seriously and are confident that our policies are fully compliant with our agreement with the FTC,"
Facebook had already been including users' photos and other information in advertisements and paid $20 million to settle a class action lawsuit over the practice. Notifying users of the advertising practice was part of that legal settlement.
—Updated with a comment from Facebook at 6:04 p.m.