Legal scholars are still trying to sift through the broader implications of the Supreme Court's recent ruling on health-care reform. Yet some experts now wonder if the precedent set by the June decision could eventually be used to weaken U.S. air pollution rules.

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In an article this week, Jonathan Adler of Case Western University argues that the Medicaid portions of last month's Supreme Court ruling could end up having far-reaching effects. Recall that under the Affordable Care Act, states were originally supposed to expand Medicaid coverage to millions of low-income individuals—otherwise, they'd lose their existing Medicaid funds. But in its June decision, the Supreme Court ruled 7 to 2 that this requirement was too "coercive." States were so reliant on their existing Medicaid funds, the Court said, that the federal government could basically force states to do anything by threatening to withhold this money. And that wasn't acceptable.

Now, as Adler points out, the Clean Air Act works in a somewhat similar fashion. States are required to submit plans to the Environmental Protection Agency to clean up their air pollution. If they don't meet certain air-quality standards, then the EPA can block a portion of their federal highway funding. As the Congressional Research Service details, the EPA has threatened states with this sanction 855 times between 1990 and 1997. And states usually respond pretty quickly—the EPA has only actually had to take away funding a handful of times over the years.

What's more, the EPA is constantly imposing new environmental responsibilities on the states. The Clean Air Act's air-pollution standards are designed to get tougher over time, as new science rolls in. Most recently, the agency declared that carbon-dioxide, which is responsible for global warming, was a pollutant that needed to be regulated just like lead or mercury. (The EPA did this in response to another Supreme Court ruling.) At some point, states will likely have to come up with their own plans for tackling their greenhouse gases. And that, notes Adler, could be seen as a heavy new burden akin to Obamacare's Medicaid expansion.

"For many states, federal highway funds represent the lion’s share of their transportation budget," Adler notes. "As a consequence, threatening to take highway funds may strike some courts as unduly coercive under NFIB."

So a state that refuses to comply with new air-pollution standards (Texas, say) could try to sue the EPA over this matter. And if the Supreme Court decided that the highway fund sanctions were overly coercive, the EPA would no longer have the ability to require states to comply.

Is this at all plausible? Legal scholars say the possibility is hard to dismiss entirely. "You could definitely imagine a governor pushing back against the EPA over sanctions," says Ann Carlson, a professor of environmental law at the University of California Los Angeles. On the other hand, she notes, states might not have standing to sue unless they're actually hit by highway sanctions—something that happens rarely.

It's also not clear whether the Supreme Court would even agree that the Clean Air Act is structurally similar to Medicaid. "There are definitely ways to distinguish the health care facts from the Clean Air facts," says Carlson.

For one thing, federal Medicaid funds makes up a much, much bigger portion of state budgets than federal highway money does. (Last year, the government spent $275 billion on Medicaid versus $40 billion on highways.) What's more, federal Medicaid funds are an entitlement program written into law—states have a reasonable expectation that they should receive the money each year as long as they're following the rules. By contrast, federal highway funding needs to get renewed constantly by Congress. It's less predictable. So states will have a harder time arguing that the federal government is pulling an unfair bait-and-switch by imposing new requirements. UCLA's Jonathan Zasloff has more on why this distinction could matter, legally, here.

Ultimately, however, the actual legal arguments may be a side issue. If there are five justices who agree that the Clean Air Act is unduly coercive, then that might be enough. "Bottom line: if the Supremes want to injure the Clean Air Act, they will injure the Clean Air Act," Zasloff writes by e-mail. "Law doesn't really matter at this point."

Carlson agrees that it would ultimately come down to votes. "The caveat here is that the health care decision is a brand-new ruling," she says, "and we still have no idea how far the Supreme Court is willing to go."