The debate over the New Alternative Transportation to Give Americans Solutions Act of 2011, or NAT GAS Act, has focused mostly on the question of whether the federal government should use hefty subsidies — $64,000 per truck — to interfere with the free-market allocation of resources. On that point, a surprisingly large number of Republicans are siding with their central-planning-advocate colleagues on the other side of the aisle.

But why are so many Democrats enamored with big corporate-welfare giveaways to the natural-gas industry in the first place? The answer might be a little-noticed provision called “Section 403” that could clear the legal path for the U.S. Environmental Protection Agency (EPA) to pursue the Obama administration’s entire energy agenda via back-door regulations.

Club for Growth president Chris Chocola first rang the alarm bell about Section 403 in a post on RedState, writing that it “lends credibility to the EPA’s ability to regulate greenhouse gas emissions.” The implications are even more profound than that.

Up to now, Congress had never approved of the EPA’s attempts to shoehorn greenhouse-gas regulation into the 1970 Clean Air Act. In fact, the House voted overwhelmingly to prohibit the EPA from doing so, and while the Senate failed to achieve a 60-vote consensus on any particular solution, 50 senators voted for outright pre-emption and another 14 voted for deeply flawed, political-cover alternatives that nonetheless objected to the EPA regulating greenhouse gases without congressional approval.

Section 403 of the NAT GAS Act accepts as a given that the EPA has the authority to regulate greenhouse gases, saying: “It is the sense of the Congress that the Environmental Protection Agency[’s] new fuel economy and greenhouse gas emission regulations for medium- and heavy-duty engines and vehicles should provide incentives to encourage and reward manufacturers who produce natural gas powered vehicles.”

The regulations it is referring to were negotiated in an infamous backroom deal in which then–climate czar Carol Browner threatened to allow states to pass their own regulations if the auto industry didn’t acquiesce to expensive new federal regulations. Mary Nichols, chairwoman of the California Air Resources Board, another party to the secret negotiations, confirmed to the New York Times that Browner took the lead. “We put nothing in writing, ever.” Nichols said.

Now the EPA is poised to take the next step and impose an absurd 62-miles-per-gallon fuel-economy standard by 2025 that will take safe family vehicles off the road and force us all to buy the tiny, underpowered, politically correct cars favored by bureaucrats. The EPA is also moving beyond regulating motor vehicles to twisting the Clean Air Act as a way to pursue the entire failed cap-and-trade energy-tax agenda, with a particular emphasis on regulating the coal industry into oblivion and sending the price of gasoline skyrocketing.

While Congress of course should step in and stop the EPA, so far it has failed to do so. That makes the dubious legal status of the EPA regulations critical. Virginia attorney general Ken Cuccinelli and Texas attorney general Greg Abbott have taken the lead with aggressive legal challenges. Texas has even refused to comply with EPA dictates it considers unlawful. There are also several private legal challenges to the EPA.

Unfortunately, Section 403 could knock the legs out from under these lawsuits by creating a clear legislative history that takes as a given the existence of EPA authority to regulate greenhouse gases. If the bill passes, EPA will argue it is conclusive proof that their authority exists, and will likely find a sympathetic ear from a judiciary that has consistently favored expansive interpretations of the Clean Air Act.

Republican proponents of the bill make a variety of arguments, contending essentially that advancing natural-gas vehicles is such a national imperative that free-market principles should be set aside and government should step in. But the biggest impact of the bill may be something entirely different and wholly unintended: a green light for the EPA’s whole agenda of skyrocketing energy prices via greenhouse-gas regulation. That’s more than enough reason to kill this bill.

— Phil Kerpen is vice president for policy at Americans for Prosperity and the author of the forthcoming book Democracy Denied (BenBella Books, October 2011) on Obama’s regulatory agenda).