The murder trial for ex-Philadelphia Police Officer Ryan Pownall, scheduled to start next week, may be delayed due to legal wrangling over a key issue after a judge on Tuesday rejected prosecutors’ request to modify what she will tell jurors about justifiable shootings by police.

The District Attorney’s Office late Tuesday afternoon said it would appeal the ruling to Superior Court, though it remained unclear how quickly the issue would be resolved. Beyond delaying the start of the trial, the outcome could influence the strategy of both sides in the first prosecution of a city cop for an on-duty shooting in two decades.

The decision relates to a motion the District Attorney’s Office filed in December arguing that the state’s current use-of-force law for police is unconstitutional, and that jurors should be given differently worded instructions that could undercut Pownall’s defense that his actions during a 2017 traffic stop in North Philadelphia were legally justified.

In her order Tuesday, Common Pleas Court Judge Barbara A. McDermott wrote that the request was essentially asking her “to judicially usurp” laws passed by state legislators.

“This court has no authority to summarily rewrite portions of a criminal statute, for doing so would serve only to supersede the will of the people as placed into the hands of the legislature,” McDermott wrote.

Pownall’s lawyers had criticized the request by District Attorney Larry Krasner’s office, saying it was an attempt to change a law shortly before trial to make its case easier to win.

Some legal experts also questioned whether the maneuver, if successful, would violate Pownall’s due process rights by retroactively applying a new criminal standard to a defendant’s past conduct.

One of Pownall’s attorneys, Fortunato Perri Jr., said in an email Tuesday that if prosecutors appealed the ruling, it would amount to an admission that their case against Pownall is not supported by current state law.

“An appeal of the court’s ruling would confirm that the district attorney has violated Ryan Pownall’s civil and constitutional rights by bringing a malicious prosecution for his own political gain,” Perri said.

Cameron Kline, a spokesperson for the District Attorney’s Office, declined to comment Tuesday.

Pownall is accused of fatally shooting David Jones on June 8, 2017, after stopping him for riding a dirt bike on a North Philadelphia street. The two men then struggled over a gun that Jones had been carrying before he broke free, and that fell to the ground when he ran away, police have said.

Pownall was fired over the shooting in 2017, with then-Commissioner Richard Ross saying Pownall had displayed “poor judgment” and violated departmental regulations for firing at the fleeing Jones.

Krasner charged Pownall with murder and related counts last year following a grand jury investigation. A judge later downgraded the case to third-degree murder, allowing Pownall to be freed on bail while awaiting trial.