The American Civil Liberties Union is threatening legal action against the city and the Honolulu Police Department over the “unconstitutional” arrest of an impaired-driving suspect who tested negative for alcohol.

The letter, sent to Honolulu Police Chief Arthur “Joe” Logan and Honolulu Corporation Counsel Dana M.O. Viola, declared the ACLU’s intention to file a lawsuit against the city and the department.

The ACLU demanded an “investigation, policy changes, and training regarding unconstitutional arrests by HPD officers” based in part on a November 2023 DUI checkpoint arrest of ACLU client Ammon Fepuleai, a math instructor at American Samoa Community College in town to help plan his cousin’s wedding, according to a news release and the letter.

No charges were filed against Fepuleai, but ACLU Hawaii Legal Director Wookie Kim wrote that the incident was “emotionally distressing and traumatizing” and that Fepuleai’s trip to Hawaii and work as a wedding planner were negatively affected.

Fepuleai had never been arrested and felt “embarrassment, shame, and humiliation.”

“Every time he sees or hears police sirens, he feels like he is about to get arrested. Mr. Fepuleai seeks policy changes within HPD that will prevent similar abuses of power in the future,” wrote Kim.

The nine-page letter delivered Monday named four officers and alleged they are “liable for false arrest without probable cause,” accusing one of turning off his body-worn camera at strategic moments.

One of the officers allegedly coerced Fepuleai to “decline to take a blood test,” which would have required him to stay overnight in police custody, and told him to post bail instead without telling him that “would mean making a legal admission that he was intoxicated, or that this would lead to the revocation of his driver’s license.”

Police allegedly falsified allegations that Fepuleai stumbled, smelled of alcohol and appeared visibly drunk.

“Mr. Fepuleai does not drink or do drugs, was not inebriated at the time of the arrest, and blew a 0.000 on a breathalyzer test, yet HPD officers still arrested him for OVUII (operating a vehicle under the influence of an intoxicant). Our investigation suggests these HPD officers fabricated their police reports to secure the arrest and justify it after the fact. These officers also improperly turned off their body-worn cameras to hide their scheme,” read the letter to Logan and Viola.

“Importantly, Mr. Fepuleai’s arrest does not stand in isolation; we understand that, in the past couple of years, at least 69 other individuals who blew 0.000 were also arrested for OVUII by HPD officers, which suggests that the City and County of Honolulu is itself responsible for having a de facto policy or widespread custom of making false arrests — despite clear indications of sobriety — as a means to justify receipt of federal grant money.”

Honolulu police made 1,302 arrests for driving under the influence through Oct. 24, according to the department’s online data dashboard.

“Both the Hawaii and the United States Supreme Courts have upheld the constitutionality of OVUII sobriety checkpoints,” Paul R. Mow, chief of staff for Prosecuting Attorney Steve Alm, told the Honolulu Star-­Advertiser.

“We have received the letter and are reviewing the allegations,” HPD spokesperson Michelle Yu said. “We will be working with Corporation Counsel to respond to the ACLU.”

The Corporation Counsel deferred comment to HPD.