T-Mobile CEO John Legere has apologized for ripping on an advocacy group, a move that earned him lots of criticism.

In defending his company’s Binge On unlimited streaming service, which the Electronic Frontier Foundation slammed as not being what T-Mobile is advertising. EFF says that T-Mobile has been “throttling” video traffic to a rate of 1.5 megabits per second, even if users didn’t sign up for Binge One and also when the network wasn’t congested, according to a CNET report.

On Twitter, EFF asked Legere directly if T-Mobile was indeed throttling video streams, and Legere, in a video response, did not mince words.

“What Binge On does, it includes a proprietary technology and what the technology does is not only detect the video stream but select the appropriate bit rate to optimize to the video, the mobile device,” he said. “That’s part A of my answer. Part B of my answer is, who the f— are you, anyway, EFF? Why are you stirring up so much trouble, and who pays you?”

The comments proved to be so controversial that one video company even stopped its participation in Binge One, prompting Legere to follow up with an open letter.

“Look, by now you know that I am a vocal, animated and sometimes foul mouthed CEO. I don’t filter myself and you know that no one at T-Mobile filters me either (no, they don’t even try). That means I will sometimes incite a bit of a ‘social media riot,’ but I’m not going to apologize for that,” he wrote. “I will however apologize for offending EFF and its supporters. Just because we don’t completely agree on all aspects of Binge On doesn’t mean I don’t see how they fight for consumers.”