Robert J. MacLean became a federal air marshal for the TSA in 2001. In that role, MacLean was assigned to protect passenger flights from potential hijackings. In July 2003, the Department of Homeland Security issued a confidential advisory about a potential hijacking plot by al Qaeda to be executed by the end of summer 2003.

A few days later, MacLean received a text message from the TSA cancelling all overnight missions from Las Vegas (where MacLean was stationed) until early August. MacLean believed that cancelling those missions during a hijacking alert was dangerous and illegal insofar as federal law required the TSA to put an air marshal on every flight that "presents high security risks." After MacLean learned from a supervisor that the missions had been canceled due to budgetary restrictions and that "nothing could be done," he contacted an MSNBC reporter and told him about the canceled missions.

Following publication of the MSNBC story, several Members of Congress criticized the cancellations and, within 24 hours, the TSA reversed its decision and put air marshals back on the flights. MacLean was subsequently fired for disclosing sensitive security information without authorization. The Merit Systems Protection Board held that MacLean did not qualify for protection because his disclosure was "specifically prohibited by law."

However, the United States Court of Appeals for the Federal Circuit vacated the Board's decision, and the United States Supreme Court in this opinion affirmed the Court of Appeals, holding that MacLean's disclosure was not prohibited by the TSA regulations because regulations do not qualify as "law" under the applicable whistleblower statute.