Binge On by T-Mobile is a throttling strategy that affects all video apps, according to an investigation by the Electronic Frontier Foundation.

T-Mobile's Binge On video offer was introduced as a free bonus that brings unlimited video streaming to its customers without hurting their data plans. The company does this by zero-rating any streaming video app that participates -- essentially making the data used while watching video on a cellular network free.

As part of T-Mobile's data-free video offering, video delivered by participating apps -- including Netflix, Hulu, Sling, and more -- is optimized to stream at roughly 480p, or DVD quality. That means Binge On video uses up less data, but hopefully still looks pretty good on a small screen.

But now, besides being questionable from a Net Neutrality perspective, Binge On is being called nothing but a friendly front for throttling all video on T-Mobile's network.

On Monday, digital civil liberties activist organization, the Electronic Frontier Foundation (EFF), published a report accusing T-Mobile of using Binge On to throttle the quality of all video content delivered via its network.

The report is a result of an investigation by the EFF in which tests were done using a Binge On-enabled LTE connection in the same location at the same time of day over several days.

Each time, EFF attempted to access video over T-Mobile's network in one of four different ways: Streaming an HTML5 video embedded from a webpage, downloading a video file directly to the SD card, downloading a video file with the file extension masked (so it wouldn't be treated as a video), and downloading a large non-video file for comparison.

Each of those tests were then performed over both an open HTTP connection and an HTTPS connection, the second of which prevented T-Mobile from recognizing any of the content -- essentially turning off Binge On.

The result? "The first result of our test confirms that when Binge On is enabled, T-Mobile throttles all HTML5 video streams... even when the phone is capable of downloading at higher speeds, and regardless of whether or not the video provider enrolled in Binge On," wrote EFF.

Furthermore, EFF says T-Mobile throttled direct video downloads even when the extension was changed to mask the file type. Finally, the organization says T-Mobile's throttled video streaming didn't even adapt to each stream ensure the video didn't stutter or need buffering. "This means T-Mobile's 'optimization' consists entirely of throttling," wrote EFF, arguing that if the practice only limits data use without controlling for quality, it isn't actually "optimization" at all.

The EFF wants the Federal Communications Commission to investigate T-Mobile's Binge On -- a program that Chairman Tom Wheeler has previously praised for being "highly innovative and highly competitive," while adding he would be "keeping an eye" on it going forward:

"We believe the FCC should regulate lightly, but our research suggests this is a significant consumer harm that runs afoul of well-established open Internet principles," wrote the EFF. "The FCC can and should step in and hold T-Mobile accountable."

On Tuesday, T-Mobile responded to the EFF's throttling charge in a statement emailed to DSL Reports, which singularly focused on semantics:

"Using the term 'throttle' is misleading... We aren't slowing down YouTube or any other site. In fact, because video is optimized for mobile devices, streaming from these sites should be just as fast, if not faster than before. A better phrase is 'mobile optimized' or a less flattering 'downgraded' is also accurate."