The Federal Communications Commission says it has had "productive" discussions with Comcast and T-Mobile USA about whether data cap exemptions conflict with the goals of net neutrality.

The FCC sent letters last month asking Comcast, T-Mobile, and AT&T to meet with commission staff by January 15. The FCC has met with Comcast and T-Mobile, but not AT&T. A meeting with AT&T has been scheduled.

"FCC staff had productive discussions with company representatives as part of a larger policy examination of trends in the market. We cannot comment on the details of individual meetings," FCC spokesperson Kim Hart told Ars.

When asked if there will be any action taken against the companies, Hart said, "This is not an enforcement action or investigation, as the Chairman [Tom Wheeler] has made clear. Direct dialogue with companies is an important way in which the Commission can watch and learn, and consistent with our approach in the Open Internet Order."

Each of the three carriers has implemented "zero-rating" in some form, exempting certain content from data caps. Consumers are more likely to use services that don't count against their data caps, so exemptions can be used by carriers to give advantages to their own online services or services from companies who pay for exemptions.

While there is no specific net neutrality rule banning data cap exemptions, the FCC enforces a general conduct standard in which it judges whether a specific practice "unreasonably interferes" with the ability of consumers to reach content or the ability of content providers to reach consumers. The FCC's letters to the carriers pointed to concerns raised by consumer advocates and requested meetings "to ensure that we have all the facts to understand how this service relates to the Commission's goal of maintaining a free and open Internet while incentivizing innovation and investment from all sources."

T-Mobile has faced the most criticism of the three carriers over its "Binge On" video program, which exempts certain video services from data caps while throttling almost all video in order to reduce data usage. Binge On is enabled by default, but customers can turn it off or back on. Video providers don't have to pay for the data cap exemption, but they do have to meet some technical criteria.

Though the FCC's net neutrality rules ban throttling, lawyers say that T-Mobile has a solid argument that Binge On's throttling doesn't violate the rule because customers can turn it off.

Comcast zero-rates its own Stream TV service, which provides online video to Internet-only customers, but says it's beyond the reach of net neutrality rules because Stream TV is an IP cable service instead of one delivered over the public Internet. Stream TV may appear similar to Netflix and other online video services because it's accessed on computers, tablets, and phones, but the live TV portion of the service works only in the customer's home.

AT&T's Sponsored Data program charges third parties, such as advertisers, for the right to deliver data without counting against consumers' mobile data caps.

Comcast today declined to comment on its meeting with the FCC. We're still waiting to hear back from AT&T and T-Mobile.

Correction: This story originally said the FCC met with all three carriers. We learned after publication that the meeting with AT&T is scheduled but hasn't yet happened.