It never fails: All major environmental regulations are met with legal challenges from polluting industries. And in the case of the Clean Power Plan, the Obama administration’s landmark regulation of carbon emissions from existing power plants, lawsuits are pouring forth like soot from a smokestack.

Opponents were so eager to express their opposition to the plan that they filed a lawsuit when it was merely proposed. That was thrown out of court for being premature. But shortly after the final rule was published in the Federal Register on Oct. 23, more lawsuits started rolling in. (Suits are also being filed against the rule governing new power plants, but since that rule takes a more traditional approach to regulating pollution, it doesn’t raise the same set of legal questions.)

Currently four groups have filed major suits opposing Obama’s plan: 24 overwhelmingly Republican state attorneys general, a coalition of business groups led by the Chamber of Commerce, coal giant Murray Energy, and some electric utilities such as Southern Co. North Dakota and Oklahoma have filed separate suits as well. The D.C. Circuit Appeals Court, which has jurisdiction over challenges to EPA regulations, will likely combine the four big suits — as well as others that continue to trickle in from additional states and groups — into one case, say experts.

Of course, the plan has many defenders too. The attorneys general of 18 other states, including populous powerhouses New York and California, on Wednesday asked the court to keep Obama’s rule in place. Cities joined the petition too, including Washington, D.C., Chicago, Philadelphia, and New York City. And last week, a coalition of environmental groups filed a motion to intervene as respondents, meaning they would work with the EPA on defending the plan in court.

The involvement of so many states, not just industry stakeholders and green groups, reflects the stark political divisions over climate policy and the incredibly high stakes. “I can’t recall a Clean Air Act rule, or other EPA rule, that had 44 states in the mix,” Joe Stanko, an attorney at Hunton & Williams, told Greenwire.

Here’s what you need to know about the cases filed against the Clean Power Plan:

The first legal threat: Will implementation be delayed?

The most immediate threat the suits pose to the rule is that they have requested that the D.C. Circuit Court issue a stay of its implementation. If that were granted, it would mean the Clean Power Plan would not take effect until the Supreme Court has determined its legality. That will take two or three years, during which time a Republican who opposes the rule could win the White House.

Every Republican presidential candidate has pledged to undo the plan, but that would be hard to accomplish unless the court issues a stay. That’s because states are already starting to draw up compliance plans, and by January 2017, they will be even further along in that process, if not done. But if the court does issue a stay, and progress on compliance plans stalls out in the next few months, it would be easier for a Republican to undo the Clean Power Plan once in the White House.

We’ll find out in a matter of weeks or months whether a stay is granted. And that decision will give some insight into whether the rule itself will be upheld or overturned, since in order to get a stay you have to convincingly argue there is a significant chance the rule will be overturned.

Petitioners for a stay also have to show that the rule will cause “irreparable harm” to the challenger while the case makes its way through the courts. Since states can easily get extensions until 2018 to submit their compliance plans, and since they don’t need to actually start hitting any emissions targets until 2022, environmental lawyers say that’s a hard case to make, and it’s therefore unlikely that their opponents can convince the court that irreparable harm would be done in the next few years.

“The stay motions, we think, are very much off-base because the rule has one of the very longest lead times in history,” says Vera Pardee, supervising attorney at the Center for Biological Diversity’s Climate Law Institute. “It doesn’t even begin to be implemented until 2022 and then has a glide path through 2030.”

But even if the court refuses to grant a stay, that doesn’t mean the rule will be upheld.

The biggest legal threat: Was the EPA too creative?

Each of the lawsuits makes a different set of arguments as to why the Clean Power rule is illegal, even unconstitutional. There is one overarching claim, though, that is central to every suit and probably the one with the best chances of succeeding: that the creative approach EPA took in devising the plan goes beyond its authority under the Clean Air Act. This is not a question of whether EPA can regulate greenhouse gas emissions; the Supreme Court already ruled that it can in the landmark 2007 decision Massachusetts v. EPA. Saying EPA can regulate carbon emissions is different from approving its specific plan to do so. That’s what is now going to be put to the test.

The Clean Power rule departs from the way air pollution is most typically regulated by the federal government. When the relevant section of the Clean Air Act was written in 1970, the target was what we now call conventional pollutants, such as mercury and lead. For that kind of pollutant, the total amount in the world’s atmosphere isn’t the only concern. The negative health effects are much more localized around the source. So you can’t just close one mercury-spewing plant while another stays open to reach your total emissions target, because that would be unfair to the people who live near the plant that remains. But in the case of carbon dioxide, it doesn’t matter where it’s produced, it’s the total amount in the atmosphere that determines how much the planet is warming. (This leaves aside, for the moment, the fact that coal-fired power plants are also major sources of conventional pollutants like mercury and smog, and that as a matter of environmental justice, the public health benefits of closing coal plants should be spread around as evenly as possible, something EPA is encouraging in the Clean Power rule.)

The basic mechanism for reducing conventional pollution is to order the factories or power plants producing it to use the best available technology to rein it in, like putting scrubbers at the top of smokestacks. This can’t really be done with carbon emissions, short of installing expensive carbon capture and sequestration (CCS) technology that has yet to be widely used on an industrial scale. So instead EPA took a more nuanced approach. Recognizing that the product coal power plants produce, electricity, can be produced more cleanly, EPA gave states a variety of options for reaching their emission-reduction goals. “The things that the EPA is looking to for emissions reductions, the three building blocks — improving efficiency at coal plants, using more natural gas than coal plants, and using more renewables — is exactly what states and utilities have been doing to reduce their emissions,” says Ben Longstreth, a senior attorney at the Natural Resources Defense Council. “The EPA is really building off trends in the industry.”

Essentially, EPA was trying to do industry a favor. The agency is giving states and electric utilities a great deal of flexibility in how they cut emissions, which is also likely to lead to reduced electricity costs for consumers. This approach would clearly be less harmful to the coal industry than if EPA simply ordered all coal plants to adopt CCS, which would render most of them too expensive to operate.

But instead of appreciating the flexibility, industry and Republicans are suing the agency and arguing that it doesn’t have the authority to develop a plan that’s so smart and versatile.

What about the Supreme Court?

No matter what the D.C. Circuit Court decides, the losing side will appeal the case to the Supreme Court. So what would happen if the Supreme Court overturned the Clean Power Plan? Under a Republican president, that would be the end of EPA’s efforts to meaningfully regulate carbon emissions from power plants. But a Democrat might respond by ordering EPA to come up with a new plan that takes a more conventional approach to controlling pollution, like ordering installation of CCS.

“In the rule, the EPA looks at the ways you can reduce carbon emissions from power plants,” says Longstreth. “It looks at CCS and says the approach they were taking is less expensive, the most cost-effective option.” But EPA didn’t find the cost of CCS is too high to make it a viable alternative. “They have definitely left the door open,” says Longstreth. And that, ironically, would actually be more damaging to the coal industry than the current plan.

Industry and Republican states wouldn’t accept a rule requiring CCS either, of course. They would challenge such a rule on the grounds that it’s too expensive, since the Clean Air Act requires that EPA adopt “the best system of emission reduction … taking into account the cost of achieving such reduction.”

“The petitioners are quite candid in saying it turns out that there’s no cost-effective, technologically feasible way to reduce carbon emissions through end-of-pipe measures like scrubbers that work for other pollutants,” says Sean Donahue, who is representing the Environmental Defense Fund in the litigation. “[Petitioners say] that is the model that Congress had in mind and it doesn’t work for CO2 and EPA just can’t do anything about it.”

Even if industry won its argument that EPA can only regulate emissions more conventionally, plant by plant rather than via a state’s whole energy system, and also won its argument that EPA can’t require CCS because it’s too expensive, the agency could devise a rule that simply requires coal plants to switch to natural gas, or run less often, or shut down. All of those options would also be more jarring to the coal industry and energy utilities that the Clean Power rule.

By suing to block the most industry-friendly approach that could have been taken, the petitioners have basically admitted there is no rule they won’t challenge.

So where does that leave us?

There are other arguments being advanced in some of the briefs requesting a stay. One is the claim, which featured prominently in the lawsuits that were filed and thrown out before the Clean Power Plan was finalized, that EPA doesn’t have the authority to regulate carbon emissions from power plants because power plants are already regulated for hazardous air pollutants like mercury. Given that the Supreme Court already ruled that carbon can be regulated as an air pollutant, that argument seems unlikely to fly.

Some petitioners are also claiming the rule is unconstitutional because it infringes upon states’ rights under the 10th Amendment, an argument that will seem far-fetched to anyone who accepts a post–New Deal definition of the Interstate Commerce Clause.

Ultimately, the court cases are likely to hinge on the big question outlined above: Can EPA make a rule that reduces emissions from coal plants not just by putting rules on the plants themselves, but by giving states targets they can hit through shifting to natural gas, renewables, and efficiency? That seems to follow the spirit of the Clean Air Act, but will the courts find that it’s within the letter of the law? The relevant sections of the act were written in 1970, before this question could even have been fathomed. It’s possible that the courts will hold that the Clean Air Act simultaneously sets a standard for what is a pollutant that compels the EPA to regulate carbon, but provides no legal mechanism for meaningfully doing so. That would mean the ball is back in Congress’ court to fix that shortcoming. Since Congress is broken and incapable of updating laws, and Republicans in Congress no longer favor clean air legislation, the prospects for that are pretty dim.

So if you care about climate change, you’d better hope the rule is upheld. Given that three of the Supreme Court justices — Samuel Alito, Antonin Scalia, and Clarence Thomas — are virtually guaranteed to vote against any Obama administration regulation, this will probably be a nail-biter like the Obamacare ruling.

If the Clean Power Plan is thrown out, the U.S. will likely be unable to meet its commitments from any deal made during the U.N. climate negotiations in Paris this December, which would in turn undermine the whole international agreement’s legitimacy.

So the stakes are incredibly high, and it’s going to be a anxious couple of years waiting to find out if the Supreme Court will let us try to avert catastrophic climate change.