More than a year after net neutrality was essentially abolished by a divided Federal Communications Commission, a major legal challenge supported by dozens of companies and advocates has its day in court tomorrow. Mozilla v. FCC argues that the agency’s decision was not just dead wrong, but achieved illegally.

“We’re not just going into court to argue that the FCC made a policy mistake,” said Public Knowledge VP Chris Lewis in a statement. “It broke the law, too. The FCC simply failed in its responsibility to engage in reasoned decision-making.”

Oral arguments before the D.C. Circuit Court of Appeals commence Friday, February 1, though the FCC attempted to have the date put off due to the shutdown — and the request was denied.

The legal challenge is one of several tacks being taken against the FCC’s replacement of 2015’s net neutrality rules with a much weaker one last year. As with any rule or law, there are multiple avenues for dissent; a direct legal challenge is among the quickest and most public.

Mozilla, along with Vimeo, Etsy, Public Knowledge, INCOMPAS, and a number of other companies and organizations, filed the challenge shortly after the new rules took effect, but these things take time to creep through the court system.

The lawsuit has a number of primary arguments against the rulemaking (you can read the full brief here), but they boil down to two basic ideas, which I’ve attempted to summarize below:

First and most important, the FCC’s entire argument that broadband is not a telecommunications service is false. This argument goes back decades, and you can read the history of it here. The short version is: telecommunication services move data from point to point, and information services do things with that data. The FCC argues that because broadband connections let you, for example, buy something online, that connection essentially is a store.

Supreme Court Justice Kavanaugh made this same very elementary mistake and was set right by a judge a couple years ago. It’s basically indefensible and no one who understands how the internet works agrees with it. As the Mozilla filing puts it, the argument “confuse[s] the road with the destination.”

The FCC also says that DNS services and caching, some of the nuts and bolts of how the internet and web work, count as information services — which is perfectly true — and that because broadband uses them, it too is an information service instead of telecommunications — which is ridiculous. It’s like saying that if a road has signs on it, the road is itself a sign. Nope. The filing again resorts to metaphor, saying “a few drops of fresh water do not turn an ocean into a lake.”

This is the primary support for the FCC’s entire case, and removing it would essentially nullify the entire new set of rules, since if the judges agree that broadband is in fact telecommunications, the industry is governed by a whole different set of statutes under the Communications Act. There are numerous other sub-arguments here that could also come into play.

Second, the FCC’s decision is “arbitrary and capricious,” and thus illegal under the Administrative Procedures Act, which requires certain standards of evidence and method to be shown in the establishment of such rules. This is supported in a number of ways, including the authority argument above. It also failed to address consumer and other complaints during the rulemaking process.

The FCC also does not justify its argument that the broadband industry is better suited to regulation by antitrust authorities, and does not justify rejection of certain other statutory authorities under which the FCC could be responsible for some of the rules. “The FCC does not adequately explain why other statutes, developed to address other problems, just happen to do the job Congress assigned to the FCC,” argue Mozilla et al.

The agency’s cost-benefit analysis, documentation required for new rules like this, is also inadequate, they argue. Certainly economic analysis of multiple major industries can be debated forever, but there are pretty basic questions unanswered or evaded here, which weakens the FCC’s entire case.

For the record, the FCC’s arguments and counter-arguments are set forth in the rule itself and court filings largely reiterate the same points.

All these arguments are not particularly new — they’ve been brought out and revised multiple times both before and after the net neutrality decision. But this is an important setting in which for them to be addressed. This panel of judges could essentially render the FCC’s rules or rulemaking process inadequate, illegal, or incorrect — or all three — and send the agency back to the drawing board.

These decisions take a great deal of time to arrive, so be ready for a wait just like the one we’ve had for the arguments to make it to court in the first place. But the wheels are in motion and it could be that in a few months’ time net neutrality will have new life.

Of course, if the FCC won’t keep net neutrality around, states will — and that’s a whole other legal battle waiting to happen.

“Comcast, Verizon, and AT&T are going to wish they never picked this fight with the Internet,” said Fight for the Future’s Evan Greer. “Internet activists are continuing to fight in the courts, in Congress, and in the states. Net neutrality is coming back with a vengeance. It’s only a matter of time.”