For years prosecutors in Louisiana’s Orleans Parish served crime victims and witnesses with documents labeled “SUBPOENA,” stamped with an official seal. The documents warned of fines and imprisonment for those who didn’t comply.

The problem, prosecutors acknowledged in 2017, was that the documents weren’t court-ordered subpoenas, as they appeared, but were devised merely to compel witnesses to come in for questioning.

Now, some people who received the fake subpoenas are suing for damages, putting to the test a 40-year-old doctrine that gives prosecutors a nearly absolute shield against lawsuits for on-the-job misconduct. The case has shined a spotlight on the wide latitude given to prosecutors to pursue convictions without the official scrutiny for potential civil-rights violations that police officers and federal law-enforcement routinely face.

Attorneys for the American Civil Liberties Union, one of the groups representing the plaintiffs, say the prosecutors’ alleged actions were so egregious that they present a perfect opening for courts to decide whether more checks and balances are needed. They presented arguments to the Fifth U.S. Circuit Court of Appeals in New Orleans on Wednesday.

The case could “establish that there is something a prosecutor can do that is so far out of the zone and so far out of their role” that courts would recognize a limit on prosecutors’ immunity, said Clark Neily, vice president for criminal justice at the Cato Institute, a libertarian Washington-based think tank.