An internal T-Mobile memo published by TmoNews says the company will begin enforcing rules against peer-to-peer (P2P) file sharing and unauthorized tethering from August 17 onward.

The terms and conditions of T-Mobile US have contained restrictions on P2P and tethering since 2008, but enforcement appears to be new. The memo says that "only customers with Unlimited High-Speed Data" will be affected, and they will be given warnings before their data speeds are reduced.

“T-mobile has identified customers who are heavy data users and are engaged in peer-to-peer file sharing, and tethering outside of T-Mobile’s Terms and Conditions (T&C)," the leaked memo states. "This results in a negative data network experience for T-Mobile customers. Beginning August 17, T-Mobile will begin to address customers who are conducting activities outside of T-Mobile’s T&Cs.”

T-Mobile's Terms and Conditions prohibit "using the Service in connection with server devices or host computer applications, including continuous Web camera posts or broadcasts, automatic data feeds, automated machine-to-machine connections or peer-to-peer (P2P) file-sharing applications that are broadcast to multiple servers or recipients, 'bots,' or similar routines that could disrupt net user groups or email use by others or other applications that denigrate network capacity or functionality."

On tethering, the terms say, "Except to the extent explicitly permitted by your Data Plan, other uses, including for example, using your Device as a modem or tethering your Device to a personal computer or other hardware, are not permitted." T-Mobile's "unlimited" high-speed data plans have a 5GB-per-month limit on tethering, which lets users share their smartphone connections with a laptop, tablet, or other Wi-Fi-capable devices.

T-Mobile's internal memo has a section called "What's Changing," which describes how the company will deal with scofflaws. It says:

Only customers with Unlimited High-Speed Data an [sic] activities outside of T-Mobile's T&C's will be addressed.

customers with Unlimited High-Speed Data an [sic] activities outside of T-Mobile's T&C's will be addressed. T-Mobile will contact these customers to explain our T&Cs and advise them that their data speed may be reduced until the next bill cycle if their behavior continues.

When contacting customers, T-Mobile will apply a Misuse Warning SOC to their [sic] until the next bill cycle, which will be reflected under the Optional Features tab of the Services Summary screen in QuikView.

to their [sic] until the next bill cycle, which will be reflected under the tab of the screen in QuikView. If the customer continues their behavior, the Misuse Warning SOC will be replaced by a Misuse Throttle SOC and their data speeds will be reduced. This will also be reflected under the Data Speed column on the Account Review screen in QuikView. Note : There will be a hover message indicating data speed reduction due to Network Abuse Management.

will be replaced by a and their data speeds will be reduced. This will also be reflected under the column on the screen in QuikView. : There will be a hover message indicating data speed reduction due to Network Abuse Management. T-Mobile has a dedicated team to assist customers with their Network Abuse Management status. After verifying the customer has been affected in QuikView, you may call the Retail Support Line or direct the customer to Customer Care for further assistance.

(We're not sure what "SOC" stands for, though it may be "System Operating Code" or "Samson Operating Code," in reference to T-Mobile's billing system.)

We've asked T-Mobile for comment but haven't heard back yet.

The Federal Communications Commission could raise a fuss about T-Mobile's practice, but it's not clear whether the commission would be willing or able to stop it. An FCC spokesperson declined to comment when asked if the commission will take action against T-Mobile.

Comcast was caught throttling peer-to-peer traffic in 2007 and agreed to stop the next year. But wireless providers are held to different standards. The FCC in 2010 passed network neutrality rules that prohibited Internet service providers from blocking applications or discriminating against Internet traffic, except in some circumstances. Those rules (which were thrown out in court and are being rewritten) contained big exceptions for wireless carriers like T-Mobile. Cellular operators were allowed to block applications as long as they didn't compete against their voice and video telephony services, and they did not have to follow the anti-discrimination standard applied to fixed Internet service providers.

Still, FCC Chairman Tom Wheeler has scolded Verizon Wireless for making network management decisions based upon "distinctions among its customers' data plans, rather than on network architecture or technology." Although Verizon was his public target because of a recent change in its policies, the FCC said it has sent letters to other wireless carriers on the same topic. Given how T-Mobile's new policy targets unlimited data, the same concerns Wheeler raised with Verizon Wireless may apply here too.

The FCC's network neutrality order from 2010 has just one rule that wasn't thrown out in court. It requires ISPs and cellular carriers to disclose accurate information about network management practices and performance, and all four major US carriers were accused of violating the rule by not being transparent about their throttling practices.

T-Mobile also throttles the top 5 percent of data users on each rate plan when they connect to congested cell sites, a policy similar to ones enforced by AT&T, Sprint, and Verizon Wireless.