Writing to the FCC on Tuesday, more than a dozen web firms and public interest groups urged FCC Chairman Tom Wheeler to launch formal proceedings that would provide opportunities for public comment on “zero rating” policies of wireless and cable Internet service providers (ISPs) that exempt streams of certain video and audio web content from monthly subscriber data caps or data charges.

Signers of Tuesday’s letter include Mozilla, Yelp and Pinterest, as well as public advocacy concerns Common Cause, Demand Progress and Access Now. Under last year’s Open Internet order in which the FCC reclassified broadband Internet services as telecommunications services while prohibiting discriminatory and other actions that block, degrade or otherwise impede the transmission of lawful content across ISP networks, the agency declined to prohibit zero rating but opted instead to assess such policies on a case-by-case basis. Although wireless carriers have touted the popularity of zero-rating with their customers, opponents contend that these offerings distort the market and give carriers the ability to favor some content over others in violation of the Open Internet rules. In response to these concerns, the FCC confirmed last fall that it had launched an investigation into the zero rating practices of three of the top four U.S. wireless carriers and one of the top-ranked national cable operators. The FCC’s probe, which is closed to third-party input, remains in progress.

Asserting, however, that any decisions the FCC makes in connection with the ongoing probe “are too important to happen behind closed doors,” the groups called for broader FCC proceedings on issues related to zero rating, as those issues “have implications for the Internet ecosystem that reach far beyond the stakeholders directly affected” by the specific carriers targeted by the FCC probe. In arguing for such proceedings, the groups advised Wheeler that, since the Open Internet order was adopted, “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.” Adding, “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,” the groups proclaimed: “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.”