A federal appeals court this week denied The Washington Post and two civil liberties groups access to a lower court opinion blocking the government from forcing a tech company to break its encryption to help law enforcement.

At issue is a September 2018 sealed opinion by a federal judge denying the government’s request to compel Facebook under the Wiretap Act to break the encryption on its popular Messenger app so that authorities could monitor the calls of members of the MS-13 criminal gang.

In February 2019, U.S. District Judge Lawrence J. O’Neill in the Eastern District of California denied a motion by The Post, the American Civil Liberties Union and the Electronic Frontier Foundation to unseal the opinion.

The newspaper and civil liberties group appealed, arguing in April that the public has a right to know a court’s reasons for restraining the government’s power to force a tech company to break its encryption. But an attorney for the Justice Department countered that unsealing the 2018 opinion would harm an ongoing investigation in California.

On Wednesday, a three-judge panel of the U.S. Court of Appeals for the 9th Circuit affirmed O’Neill’s denial.

“The documents [sought] have not historically been open to the general public during an investigation,” the panel wrote. “And because of the ongoing nature of the investigation, the benefits of open proceedings are ‘more than outweighed by the damage to the criminal investigatory process,’ ” quoting an opinion from a 1989 case.

The issue of how a company reconciles its obligation to provide technical assistance to government investigations with its duty to protect user privacy and security is at the heart of a long-running national debate.

Several years ago, the Justice Department and Apple squared off in a high-profile legal showdown over the same issue, when the government sued Apple to break into a dead terrorist’s locked iPhone. The department backed off when the FBI found a way to hack the phone without having Apple undermine its device encryption.

“It’s disappointing and frustrating because the justification for the sealing was also sealed and yet we knew the matter pertained to more than a dozen indicted cases,” said Duffy Carolan, The Post’s attorney in the case. “Once a case is indicted, the investigatory interest should give way to the public’s right of access.”