According to AT&T, the users who would be affected by the change use about 12 times more data than the average smartphone user.
“These customers can still use unlimited data and their speeds will be restored with the start of the next billing cycle,” AT&T said in a statement on Friday. “Before you are affected, we will provide multiple notices, including a grace period.”
AT&T said users in the top 5 percent typically stream video and music using their wireless network instead of Wi-Fi.
"You can send or receive thousands of emails, surf thousands of Web pages and watch hours of streaming video every month and not be in the top 5 percent of data users," AT&T said.
Public advocacy group Public Knowledge bashed the announcement on Monday.
"AT&T's announcement that it will throttle the wireless service of so-called 'heaviest users' of its wireless service is simply the latest example of Internet rationing, an anti-consumer, bait-and-switch tactic being used by Internet service providers,” said Harold Feld, legal director for Public Knowledge.