The director Michael Moore says that a federal judge’s ruling to allow Chevron to subpoena footage from the documentary “Crude” could have dire consequences on the documentary filmmaking process, and urged that film’s director to resist the subpoena if he can.

On Thursday, Judge Lewis A. Kaplan of United States District Court in Manhattan said that Joe Berlinger, the director of “Crude,” would have to turn over more than 600 hours of footage from that documentary. The film chronicles the Ecuadorians who sued Texaco (now owned by Chevron) saying an oil field contaminated their water. Chevron said that Mr. Berlinger’s footage could be helpful as it seeks to have the litigation dismissed and pursues an international treaty arbitration related to the lawsuit.

In a telephone interview on Thursday night, Mr. Moore, whose films include “Bowling for Columbine” and “Capitalism: A Love Story,” said that he had never heard of such a ruling.

“If this isn’t overturned, it would make a lot of documentary filmmakers afraid,” Mr. Moore said. “People are going to have to start getting rid of all their extra footage now, right?”

Should the decision of Judge Kaplan be upheld and a subpoena be served for Mr. Berlinger’s footage, Mr. Moore said, “The chilling effect of this is, someone like me, if something like this is upheld, the next whistleblower at the next corporation is going to think twice about showing me some documents if that information has to be turned over to the corporation that they’re working for.”

Mr. Moore said that in making his documentary films like “Roger & Me,” he has spoken in confidence to corporate employees who have revealed sensitive information or shared internal documents.

“I’ve never had to deal with any corporation suing me to find out how I gather this information,” he said. “Obviously the ramifications of this go far beyond documentary films, if corporations are allowed to pry into a reporter’s notebook or into a television station’s newsroom.”

Mr. Moore said he hoped the judge’s ruling would be overturned on appeal, and said that if it is not Mr. Berlinger should resist the subpoena “if he can.”

“I think that he’ll find that he’ll have the support of hundreds of filmmakers who will back him in this,” Mr. Moore said.

“Documentaries are a form of journalism,” he added.

The lawyers for Mr. Berlinger said they would ask Judge Kaplan to stay the subpoena while they appeal the decision.