Reed Hastings, co-founder and CEO of Netflix, delivers a keynote address at the 2016 CES trade show in Las Vegas, Nevada, Jan. 6, 2016. Reuters/Steve Marcus

Streaming service Netflix said it has been throttling its video for AT&T and Verizon customers using wireless networks for more than five years, reported the Wall Street Journal Thursday. Netflix said it has been lowering the quality of its video, capping it at 600 kilobits per second, in order to to “protect consumers from exceeding mobile data caps,” the Journal reported.

Six hundred kilobits per second is far slower than should be possible, but Netflix said that watching two hours of HD video would consume six gigabytes of data, which would use up the entire data allowance on an $80 monthly Verizon plan. Netflix said it feared customers would drop the service if it ate through all of their data. The streaming service said it doesn't throttle video for T-Mobile or Sprint because "historically, those two companies have had more consumer-friendly policies."

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The throttling issue became a topic for discussion last week after T-Mobile's CEO accused his rivals of lowering the video quality. A Verizon spokesman told the Journal it "delivers video content at the resolution provided by the host service, whether that’s Netflix or any other provider," while AT&T’s senior executive vice president of external and legislative affairs said they were "outraged to learn that Netflix is apparently throttling video for their AT&T customers without their knowledge or consent.”

The Verizon spokesperson continued: "Verizon delivers video content at the resolution provided by the host service, whether that’s Netflix or any other provider."

Netflix is a major hub for internet consumers, accounting for about 37 percent of all bandwidth consumed by North American Web users during prime time, according to the Canada-based network firm Sandvine. Netflix reportedly accounts for an estimated 3.4 percent of data traffic for mobile networks; and it has grown quickly, surpassing 75 million subscribers worldwide this year.