Wireless carriers like AT&T and T-Mobile appear to slow down connection speeds for customers watching Netflix and other online streaming services, according to a newly released research.

Researchers from the University of Massachusetts Amherst and Northeastern University ran 650,000 tests within the U.S. from 2018 to 2019 to see if wireless carriers were slowing down (or “throttling”) streaming services.

According to the report, throttled Netflix 70% of the time and YouTube 74% of the time, but didn’t slow Amazon Prime video at all. Meanwhile, researchers discovered T-Mobile throttled Prime video 51% of the time, but didn’t bother with Skype and only occasionally slowed down Vimeo.

The study ran between January 2018 and January 2019, before and after the repeal of net neutrality regulations.

Wireless carriers usually claim that heavy online video usage can lead to slower speeds, but the research seems to show that the throttling happened consistently, regardless of peak user times.

Critics have questioned whether wireless carriers treat all internet traffic equally, which had been required under net neutrality regulations repealed last year by the FCC. The rules were enacted by the Obama administration in 2015 and required internet service providers to give equal access to all websites, without giving preferential treatment or blocking them.