Verizon's pushing back against regulators' concerns that the company may be unfairly discriminating against some of its heaviest data users. In a letter to the Federal Communications Commission obtained by the Washington Post, Verizon argues that its planned policy to temporarily slow down 4G LTE users who are on unlimited plans if they consume too much data is "narrowly tailored and appropriately targeted."

"A small percentage of the customers on [unlimited data] plans use disproportionately large amounts of data," Verizon wrote. "Unlike subscribers on usage-based plans, they have no incentive not to do so during times of unusually high demand."

The FCC last week cried foul on Verizon's plan, which takes effect in October and throttles the top five percent of unlimited data users during times of peak usage. Commission chairman Tom Wheeler blasted the company over its claims that the practice was necessary for network management.

"'Reasonable network management' concerns the technical management of your network," Wheeler wrote. "It is not a loophole designed to enhance your revenue streams."

Verizon's letter to the FCC points out that all wireless carriers have implemented some form of data throttling in response to excessive usage, and that Verizon's way of doing it is actually superior.

"The FCC has expressly endorsed the type of targeted congestion management practice that we employ as a form or reasonable network management," the letter reads. "Providers throughout the industry have employed similar (and often less tailored) versions of this same practice."

The FCC said Tuesday it had received Verizon's letter and was reviewing it.

The economics of mobile data are still considered very different from those of fixed broadband, even though in some cases you might find that LTE is a perfectly viable alternative to Wi-Fi or a wireline connection. Wireless data requires the use of wireless spectrum, the invisible airwaves that carry information from your handset to the cell tower. Unlike cables, which you can upgrade and lay more of, there's only so much spectrum to go around, and everyone from your employer to the military is trying to squeeze their wireless communications through it. (Wireless companies are expected to bid on rights to much more spectrum in a major government auction next year.)

Due to the limits of spectrum, wireless carriers have gotten much more leeway to implement data caps, throttling and other policies in response to congestion. There's evidence that data caps are increasingly spreading to fixed broadband, too — which has led some lawmakers, such as Rep. Anna Eshoo (D-Calif.), to draw a connection between these data policies and the bigger fight over net neutrality.

But key to this dispute is Verizon's decision to treat unlimited data customers differently from those on metered plans. Verizon's new policy risks undermining its earlier promise to give consumers a truly unlimited data experience, said Ed Felten, a technologist and professor at Princeton University.

"It's unsurprising that carriers are doing throttling when the networks are facing congestion," said Felten. "The question is who's being throttled. … The practices of Verizon that Chairman Wheeler is questioning has to do with throttling people preferentially based on whether they have an unlimited plan."