A sitting Brooklyn Supreme Court justice has been arrested for attempting to obstruct a federal investigation into a multimillion-dollar fraud scheme at the Municipal Credit Union — where she once served as chair of the board of directors, authorities said.

Civil judge Sylvia Ash was arrested at LaGuardia airport before appearing in Manhattan federal court to face charges of conspiracy to obstruct justice and obstruction of justice.

The 62-year-old — who is the presiding judge of the Commercial Division in Kings County — is accused of helping MCU’s former CEO, Kam Wong, cover up Wong’s own embezzlement while at MCU.

Prosecutors claim Ash tried to help explain away Wong’s expenditures and deleted text messages and emails sought as part of the investigation.

Wong previously pleaded guilty for his role in the scheme.

Ash served on the board of MCU — New York’s oldest credit union — voluntarily from 2008 to 2016.

She was released on $500,000 bond, secured by $100,000 and subject to electronic monitoring and other conditions.

Defense attorney Roger Archibald said his client would be “exonerated, because she didn’t do anything wrong.”

Meanwhile, prosecutors also announced the arrest of former NYPD officer Joseph Guagliardo, who’s accused of pocketing $250,000 during his time as a member of MCU’s supervisory committee by submitting phony security-related invoices for a company he owned. He allegedly pocketed another $200,000 from the institution by overbilling them for web-advertising.

The ex-cop is also charged with selling unspecified prescription drugs to Wong.

Court Spokesman Lucien Chalfen said Ash, who makes around 210,000 annually, was suspended with pay.

She’s due back in court Nov. 1, and faces up to 20 years in prison if convicted.