The First Amendment protects public employees from job retaliation when they are called to testify in court about official corruption, the Supreme Court ruled Thursday.

The unanimous decision cheered whistleblower advocates, who said it could encourage more government workers to cooperate with prosecutors in public fraud cases without fear of losing their livelihoods.

The justices decided in favor of Edward Lane, a former Alabama community college official who says he was fired after testifying at the criminal fraud trial of a state lawmaker. Lower courts had ruled against Lane, finding that he was testifying as a college employee, not as a citizen.

Writing for the court, Justice Sonia Sotomayor said Lane's testimony was constitutionally protected because he was speaking as a citizen on a matter of public concern, even if it covered facts he learned at work.

In past cases, the court has said that public employees generally do not have free-speech rights when they discuss matters learned at their jobs. But Sotomayor said sworn testimony in judicial proceedings "is a quintessential example of speech as a citizen for a simple reason: Anyone who testifies in court bears an obligation, to the court and society at large, to tell the truth."