BURLINGTON, Vt. (AP) – Preparing for a landmark trial on states’ ability to regulate carbon dioxide spewing from cars, a federal judge has signaled he will be slow to grant car companies’ requests for secrecy.

“Only in the most extraordinary situation will this court justify closing a trial to the public and the press,” U.S. District Judge William Sessions III wrote in a decision released Friday.

“Any request to close a courtroom for a portion of a trial challenges one of the most vital principles upon which our judicial system is founded: the presumption of public access.”

The underlying case, set for a trial to start April 9, concerns new standards in California and several northeastern states requiring car companies to reduce emissions of carbon dioxide, a greenhouse gas tied to global warming.

The companies argue the states lack jurisdiction to impose the requirement. They maintain the only way to reduce carbon dioxide emissions is to improve vehicle fuel efficiency, and that federal law leaves regulating efficiency to the federal government.

The states argue that they have legal authority to regulate emissions, and say that’s what they’re trying to do with carbon dioxide.

Three Vermont auto dealers and industry heavyweights including General Motors Corp., DaimlerChrysler Corp. and two trade groups are suing the state over its regulation. Vermont has support from the state of New York and environmental groups.

A federal judge in California, faced with a similar suit there, decided to put it off until the U.S. Supreme Court rules in a pending case about whether carbon dioxide is a pollutant subject to regulation by the Environmental Protection Agency, said Vermont Attorney General William Sorrell. That decision is expected before the court’s current term expires June 30.

The Supreme Court case is “a first cousin” to the one about to go to trial in Vermont, Sorrell said, but Sessions determined that there were enough issues in the Vermont suit unlikely to be touched by the Supreme Court to go ahead with a trial.

That shifted the focus of attention in the national debate about states’ ability to regulate vehicle carbon dioxide emissions to the federal courthouse in Burlington.

“This is a really big deal,” the attorney general said of the upcoming trial.

Industry lawyers asked that significant parts of the trial, as well as evidence submitted to the court, be kept secret. They argued that the companies needed to share with the court competitively sensitive information about the technologies and designs they might use to meet the new carbon regulation and the regulation’s economic impact.

In Friday’s ruling, Sessions said the car companies may be able to demonstrate that some information should be kept confidential, but said company lawyers must make a separate filing for each item they want to keep secret.

Charles Territo, a spokesman for the trade group Alliance of Automobile Manufacturers, said the plaintiffs were evaluating the decision and would not comment until a follow-up hearing set for Monday.

“We’re still in the process of reviewing it,” he said. “If we have anything to say about it, we’ll say it at the hearing.”

The Burlington Free Press had opposed the push for secrecy. The newspaper’s lawyer, Bob Cain, called Sessions’ decision a good step toward keeping the trial open.

“Who knows how this thing is going to pan out in the end?” Cain said. “This is just the first battle – that we’ve clearly won.”

Copy the Story Link