New York Times

WASHINGTON — The Supreme Court ruled on Wednesday in favor of a fired air marshal, saying he was covered by a federal law protecting whistle-blowers.

Chief Justice John G. Roberts Jr., writing for the majority in the 7-to-2 decision, said that the ruling might create security problems by entrusting the confidentiality of sensitive security information to “the idiosyncratic judgment” of each of the Transportation Security Administration’s employees, but that Congress could address the issue by amending the law. The president could also prohibit disclosure of the information by executive order.

“It is not our role to do so for them,” Chief Justice Roberts wrote.

In 2003, the air marshal, Robert J. MacLean, received a secret briefing from the T.S.A. about a terrorist threat affecting long-distance flights involving weapons smuggled onto aircraft in cameras and children’s toys. Two days later, he received a text message from the security agency saying that it was canceling assignments that required an overnight stay in order to save money.

Mr. MacLean complained to his superiors, saying the move would imperil public safety because air marshals would be absent from some important flights. They responded that the cuts were required by a budget shortfall.

He next went to the inspector general’s office of the Department of Homeland Security. A special agent there told him that there was “nothing that could be done.”

When those officials did not act, he contacted a reporter for MSNBC. The resulting news coverage caught the attention of members of Congress and promptly led to a reversal of the travel policy.

The government identified Mr. MacLean as the source of the report and fired him for disclosing sensitive information without authorization. Mr. MacLean challenged his dismissal under the Whistleblower Protection Act, which insulates federal workers from retaliation if they disclose “a substantial and specific danger to public health or safety.”

The whistle-blower law has an exception for disclosures “specifically prohibited by law.” The question in the case was whether an agency regulation prohibiting disclosure of “specific details of aviation security measures” was the sort of exception that Congress was referring to in the whistle-blower law.

Chief Justice Roberts rejected the argument that the word “law” as used in the whistle-blower statute encompassed the regulation. He reasoned that the statute had used the word “law” in isolation in the relevant provision, while the rest of the statute often used the broader phrase “law, rule or regulation.”

He also disagreed with the government’s contention that some regulations should nonetheless count as law because they were “promulgated pursuant to an express congressional directive.”

“Outside of this case, however, the government was unable to find a single example of the word ‘law’ being used in that way,” the chief justice wrote. “Not a single dictionary definition, not a single statute, not a single case. The government’s interpretation happens to fit this case precisely, but it needs more than that to recommend it.”

Justice Sonia Sotomayor, joined by Justice Anthony M. Kennedy, dissented in the case, Department of Homeland Security v. MacLean, No. 13-894. Justice Sotomayor wrote that the law’s mandate that the T.S.A. “shall proscribe regulations” was enough to exclude Mr. MacLean from the protections of the whistle-blower law.