Zero-rating — that thing where a company can exempt some services from data caps, to encourage customers to use it instead of other services — is still a big question mark, legally speaking. Is it “innovative” and “competitive” or does it violate net neutrality? The jury (or really, the FCC) is still out on that one, but a new formal complaint may finally force their hand toward some kind of decision.

In a petition to the FCC (PDF), the advocacy group Public Knowledge has formally complained to the commission about one particular data cap exemption: Comcast’s.

Comcast’s over-the-top broadband video service, Stream, launched in 2015 and does not count against the data cap that Comcast subscribers are increasingly subject to.

According to Public Knowledge, that exemption is a straight-up violation of the merger conditions the FCC placed upon Comcast when allowing them to buy NBCUniversal back in 2011, and is “inconsistent” with the Open Internet Rule (net neutrality).

“Comcast’s violations are not merely technical violations,” the complaint reads. “Comcast’s actions could harm consumers by turning the online video distribution marketplace from an open and competitive market to one dominated by cable incumbents such as Comcast.”

Comcast has admitted that their data caps are more about revenue than about actual network management, Public Knowledge points out, but “the business justification seems clear: the cap is set in such a way that viewers cannot easily stop using Comcast video services without accruing financial penalties.”

The problem with Comcast specifically stems from their vertical integration, they continue: “Comcast is taking advantage of its position as an infrastructure provider to ensure that the dominance it enjoyed in traditional cable services extends online.”

Giving Comcast an edge means taking other providers out of play, the complaint continues, which therefore reduces competition. And reducing competition, of course, drives up prices and reduces services for consumers.

In a statement, John Bergmayer, Senior Staff Attorney at Public Knowledge, said, “When Comcast bought NBC-Universal, both the FCC and Department of Justice recognized that Comcast could take steps to unfairly disadvantage online video. Among other things, both agencies prohibited Comcast from excluding its own services from data caps or metering, and required it to count traffic from competing online video services the same as its own. Comcast’s behavior violates the plain terms of its merger commitments and the consent decree.”

The FCC has so far been undecided on zero-rating programs. They do not violate the letter of the Open Internet Rule, but they may or may not violate its spirit. The commission has promised to take a case-by-case approach, but so far that consists mainly of polite conversations with ISPs to talk about their plans so far.

With an actual complaint now filed — against Comcast no less — the commission will have to come to some sort of finding one way or the other, which would likely then become a precedent wielded in future cases as well.