Oral arguments will begin today for one of the most important cases in internet law history. The case will be heard in a Washington, DC courtroom, as a group of net neutrality defenders squares off with the Federal Communications Commission in a legal battle to decide the rules of the web.

When the FCC, led by a Republican majority, moved in late 2017 to repeal Obama-era net neutrality rules, it kicked off a fight on several fronts. There’s been some pressure on congressional lawmakers to overrule the decision, and states have moved to implement their own versions of the rules.

But what may be the most likely shot at restoring net neutrality regulations will come from a petition against the FCC filed by several supporters of the dismantled rules. The case, Mozilla Corporation v. FCC, will be heard by the US Court of Appeals for the District of Columbia, and the court will decide whether the FCC, led by Chairman Ajit Pai, was within its rights to end the protections.

Information service versus telecommunications service

The case will hinge on deeply technical arguments. When the 2015 rules were passed, the FCC moved to regulate the internet as a telecommunications service, as opposed to the less stringent classification of an information service, a change that was then reversed in 2017. The agency has positioned that move as well within its purview, and as a return to the pre-2015 rules of the road. But in convincing the three-judge panel overseeing the case, the agency will also have to argue why it should be allowed to undo rules the same court previously upheld.

Gigi Sohn, an adviser to the petitioners in the case and former FCC senior adviser to Democratic Chairman Tom Wheeler, says in response that the FCC violated the letter of the law when it reclassified the service. By failing to adequately assess broadband service providers’ role as telecommunications providers under the FCC charter, the FCC overstepped.

“The main argument against, or number one, is the FCC violated the Communications Act when it ruled that broadband internet access service is an information service that has no telecommunications component at all,” Sohn says. In a legal brief, the petitioners have argued that the FCC’s decision would be like categorizing the road to a hotel as the hotel itself. (Citing precedent, the agency has dismissed the use of “warring analogies.”)

“Arbitrary and capricious”

The petitioners in the case have also argued that the FCC’s decision to overturn the rules has been “arbitrary and capricious” under the law. The agency can’t make a decision based only on its whims, so it has pointed to data that it says shows investment in broadband went down when the net neutrality rules were put in place. The petitioners have argued that the FCC used a flawed analysis when it made that claim.

Sohn argues that fully upending the rules at the level that the agency did was unprecedented. “No Republican or Democratic FCC has ever done that in the past,” she says. In a brief with the court, the petitioners have argued that the change “swept aside everything in its path, including the law, the facts, reasoned decisionmaking, and the decisions of this Court.”

Fundamentally, the court’s decision could also turn on deciding how much leeway the FCC has to make rules as it pleases: what kind of discretion should the agency be given under the law? The agency cites precedent that it says gives it substantial leeway to make its decisions, and the petitioners will argue over how far those boundaries go.

What else to expect

While not quite as key to the overall case, the parties in the case will likely also field several other arguments with the court. Santa Clara County, for example, has said the FCC failed to adequately consider public safety when it made its decision. (In the process, the county also produced documents about Verizon dropping its service during a wildfire crisis.)

“Mozilla filed this lawsuit because fighting for a free, open and competitive internet is part of our DNA,” Mozilla COO Denelle Dixon said in a statement this week. “Net neutrality is still an essential consumer protection that everyone online deserves, and this case is the fight to save it. We are confident that the FCC’s repeal lacks legal and factual support, and we look forward to having our case heard in court.”

Other efforts have been unfolding to reestablish net neutrality protections, and at least some will continue while the federal case is heard. Dozens of states have fielded their own net neutrality legislation, and California passed a tough version of the regulations. The latter triggered a lawsuit from the Justice Department arguing that the state was attempting to “frustrate federal policy.” Whatever decision the federal DC court comes to, though, the result will reverberate, shaking up more than one fight over the fate of the internet.