Nearly every U.S. cell provider engages in throttling, also known as slowing service selectively, according to research from Northeastern University and the University of Massachusetts Amherst.

Researchers found throttling to be pervasive on video streaming apps. What’s more, cell carriers will throttle one streaming app on a user’s phone while leaving another alone, in violation of what has become known as “net neutrality.” That’s a nickname for Obama-era regulations that required internet providers to treat all online content the same.

The FCC voted to repeal net neutrality in late 2017. The repeal took effect in June of 2018, but researchers detected throttling of select apps before then.

David Choffnes, assistant computer and information science professor at Northeastern, is spearheading the research, which has not yet been published. When the FCC codified net neutrality principles in 2015, Choffnes began developing an app to detect when cell carriers violated the rule. Since then, Choffnes’ team has conducted more than half a million tests in 161 countries to determine how often providers throttle traffic and when they slow down certain apps instead of others.

They’re throttling video traffic even when the network doesn’t need to. It happens 24/7, and in every region where we have tests.

Internet providers say they slow traffic when networks become congested. But Choffnes found that carriers are also throttling when networks are relatively clear. Some internet users may also experience throttling more than others depending on their mobile data plans.

“They’re throttling video traffic even when the network doesn’t need to,” he told the Northeastern news blog. “It happens 24/7, and in every region where we have tests.”

Choffnes’ app tested most U.S. wireless carriers. He found that AT&T throttles NBCSports, Netflix, and YouTube at roughly the same rate. That’s according to the limited findings that have been released ahead of the full report. Sprint and T-Mobile throttle YouTube and Amazon’s video streaming service more than others, the researchers found.

Choffnes says the full report will include data on how throttling changed after net neutrality was repealed but his team is not making that public yet.

“I’m not sure that the interesting question is how much it increased, but rather what exactly is getting throttled, how are the carriers doing it, what might be the impact on applications, and are any of these practices anticompetitive,” Choffner told GeekWire. “This is also something we are covering in our ongoing work, and the answers are not encouraging.”

Choffnes reported his findings to the Federal Trade Commission, the agency empowered to regulate the internet in a post net neutrality world. He plans to publish the full report in early 2019.