That thing where an ISP — like your wireless or cable company — can exempt certain services from counting against your data cap is called zero-rating, and it exists in a weird regulatory space. There are no rules against it, but there are also no rules explicitly permitting it. The businesses that do it, of course, say it is “innovative” and “competitive.” The FCC hasn’t openly decided whether or not it agrees. So a whole huge group of consumer advocates, business advocates, and businesses have gotten together to ask the FCC officially, and publicly, make up its mind.

The letter (PDF), delivered to the FCC on Tuesday, says that more than a year after the new Open Internet Order (net neutrality) was put in place, it’s time for the FCC to start a public process to decide if zero-rating is fair play or not.

“In the Open Internet Order, the FCC declined to issue a bright-line rule against zero-rating, noting a lack of consensus on the issue in the record,” the letter reads. And that’s true; zero-rating plans were fewer and farther between even as recently as a year or two ago.

“However,” it continues, “in the time since the Order was released, ISPs have created a broad enough set of test cases that a decision on each of them would have much the same effect as a new rule, only without the same public participation and transparency. Making decisions on these cases would set precedents for future practices, and would have implications for the internet ecosystem that reach far beyond the stakeholders directly affected by these individual plans.”

The FCC is, to some extent, already examining zero-rating. Although Commission chairman Tom Wheeler has called the practice “innovative” and “highly competitive” on the record, the commission has also had T-Mobile, AT&T, and Comcast come to their offices for a little sit-down chat about their exemptions.

At least one legal expert has opined that T-Mobile’s Binge On zero-rating program falls afoul of the net neutrality rule. Meanwhile, zero-rating programs continue to proliferate.

T-Mobile has both Music Freedom and Binge On, which exempt, respectively, several music and video apps from counting against data caps.

AT&T, meanwhile, offers separate-but-related sponsored data, and is pursuing plans to work out deals with certain video apps to charge them for exemption from data caps as well.

Zero-rating also happens in home, wired broadband, too. Comcast recently launched a pilot streaming-only service, and it, naturally, is exempt from Comcast’s data caps, where services like Netflix are not.

The catch is, though, that none of the FCC’s action is currently a public rulemaking process like net neutrality was. And what the groups that signed the letter really want is a chance to have their say.

“We urge you to open a public process to inform your evaluation of existing zero-rating plans,” the letter concludes.

“The FCC’s process in this critical area would be immeasurably enriched by the participation of diverse stakeholders, many of whose input helped shape the Open Internet rules. Together, we stand ready to contribute to your careful evaluation of this important issue, to protect an open internet where innovation, competition, and civil rights can thrive.”

A total of 58 groups and individuals signed on the letter. The list of internet businesses involved includes Reddit, Yelp, Kickstarter, Etsy, Medium, Meetup, and Foursquare, among many others. Alongside the businesses are a whole host of digital and consumer advocacy groups, including Common Cause, Engine, and Fight for the Future.