Former Fox News investigative reporter Catherine Herridge suffered another courtroom setback on Monday after a federal appeals court refused to pause enforcement of a contempt order that could leave her paying $800 a day for refusing to identify confidential sources.

The DC Circuit Court of Appeals denied Herridge’s request to stay issuance of its mandate while she seeks Supreme Court review, according to a brief order filed on Monday.

The ruling marks the latest defeat for Herridge in a yearslong legal battle stemming from her 2017 reporting at Fox News on Yanping Chen, a Chinese-American scientist who was the subject of an FBI counterintelligence investigation.

Last September, the appeals court upheld a district court’s contempt order against Herridge after she refused to reveal the identity of the source who leaked information used in her reporting.

Herridge has argued that identifying confidential sources would undermine core First Amendment protections for journalists and chill investigative reporting.

The dispute traces back to a lawsuit Chen filed in 2018 accusing the FBI of unlawfully leaking protected information about her to damage her reputation.

Herridge’s reporting detailed Chen’s prior service in China’s People’s Liberation Army before she emigrated to the United States more than four decades ago.

It also reported that Chen had been questioned by the FBI over alleged misstatements on immigration forms and examined her work connected to China’s space program.

As part of a counterintelligence investigation that lasted six years, the FBI searched Chen’s home. Chen, who has denied suggestions that she spied for China, was never charged with a crime.

Unable to identify the alleged government leaker after deposing dozens of witnesses, Chen subpoenaed Herridge and Fox News in an effort to uncover the source.

In February 2024, US District Judge Christopher Cooper held Herridge in contempt after she repeatedly refused to answer questions during a deposition about her confidential source.

The judge imposed a coercive civil fine of $800 per day until she complies with the order.

The ruling does not necessarily mean Herridge immediately began accruing the court-ordered sanction.

The appeals court denied her request to keep its mandate on hold while she seeks Supreme Court review, but the mandate generally does not issue until several days later, meaning the $800-a-day civil contempt fine may not yet be running.

The Post has sought comment from Herridge, her attorney and Fox News.

After the appeals court upheld the contempt order last year, the Freedom of the Press Foundation called the decision “a significant blow to press freedom for all journalists.”

Fox News similarly warned that “forcing a journalist to reveal a source not only threatens press freedom but chills investigative reporting that holds the powerful accountable.”

Herridge’s attorney, Pat Philbin, previously said she “remains committed to protecting reporters’ First Amendment rights and confidential sources.”

Chen’s attorney, Andy Phillips, welcomed the appellate court’s earlier ruling, saying that “two federal courts have now agreed that Catherine Herridge has no privilege to continue to shield the identity of a federal official who broke the law and leaked protected materials.”

Fox News is run by Fox Corp., sister company to The Post’s corporate parent News Corp.