The high court’s stance on this issue will be tested again on Monday as it hears the case of a public employee who claims he was fired after testifying truthfully against an Alabama state legislator who never showed up to work.

The case stems from the termination of Edward Lane, who, starting in September 2006, worked as director of the community intensive training for youth (CITY) program at Central Alabama Community College. Prior to that job, Lane had audited CITY’s finances and realized that then-state representative Suzanne Schmitz was listed on CITY’s payroll but was not coming into work. After the community college hired him as CITY’s director, Lane fired Schmitz when she refused to change her ways.

There’s no dispute that Lane was acting within his duties when he fired Schmitz; what’s in question is what happened next.

MORE: Why I like Buffett’s tax strategy more than Apple’s

Following her termination from CITY, Schmitz became the subject of an FBI investigation, and Lane was subpoenaed to testify at a subsequent criminal trial in which Schmitz was charged with mail fraud and fraud involving a program receiving federal funds.

Lane testified that he fired Schmitz because of her failure to come to work and perform her job at CITY.

Four months later, Central Alabama Community College President Steve Franks fired Lane for what Franks says were financial reasons. Twenty-eight other employees were let go at the same time, but Franks rescinded those terminations. He failed to bring Lane back because Lane’s position had been probationary all along. (Franks has argued that Lane’s testimony played no role in his termination, but the case has progressed nonetheless.)

Lane filed suit, claiming that he was terminated in retaliation for his testimony — an act that violated his First Amendment right to free speech.

Last summer, the Eleventh Circuit Court of Appeals affirmed a district court’s decision that Lane’s testimony against Schmitz was made as part of his official duties as CITY’s director — a government job — and not as a citizen. The appellate court ruled that to rightly claim retaliation for protected speech under the First Amendment, a public employee must show that he spoke as a citizen on a matter of public concern.

In taking his case to the Supreme Court, Lane is up against tough legal precedent. In 2006, the Supreme Court dealt with this same issue in a case in which Richard Ceballos, a deputy district attorney for the Los Angeles County District Attorney, claimed that he was subject to retaliation after he gave testimony at a trial that an affidavit to obtain a critical search warrant was false. In that case, the Supreme Court ruled 5-4 that because Ceballos was a government employee, speech he made related to his office was not protected by the First Amendment.

MORE: Can the police search your cellphone without a warrant?

Groups with a stake in the case — like the ACLU and the National Whistleblower Center, a nonprofit organization dedicated to the protection of employees who report misconduct in the workplace — have argued that the pursuit of justice is always of public concern, and therefore any testimony made at trial should be protected by the First Amendment. The Whistleblower Center said in its amicus brief in support of Lane that employees should be able to testify before federal grand juries and in criminal proceedings without intimidation. Evidence in federal criminal proceedings, like the one in which Lane testified against the state representative, the organization said, “is unquestionably a matter of ‘public concern.’”