Washington (CNN) More than 20 Democratic lawmakers have recently asked a federal appeals court to invalidate President Donald Trump's pardon of former Arizona Sheriff Joe Arpaio.

Arpaio, who was sheriff of Maricopa County, Arizona, was found in contempt of court in 2017 because he continued to make immigration arrests after a court ordered him to stop. But before he could be sentenced, Trump pardoned him.

The brief, filed last week on behalf of Democrats including Reps. Jerry Nadler, Eric Swalwell and Jackie Speier and obtained by CNN, urges "the Court to hold the President's pardon of Defendant Joseph M. Arpaio to be an invalid encroachment on the authority of the Judiciary and remand to the District Court to proceed to sentencing."

"The power to impose sanctions for contempt of court is an inherent power that is essential to the independence of the judiciary," the brief reads.

The brief was filed to the 9th US Circuit Court of Appeals by the counsel for the group of congressional Democrats, former Rep. Brad Miller of North Carolina and attorney Spencer G. Scharff.

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