One of the highest-ranking members of the Denver Sheriff’s Department fired after an alleged incident of preferential treatment is suing the city of Denver and the Executive Director of Safety, Stephanie O’Malley.

Captain Frank Gale was fired in 2015 for what the city called “commission of a deceptive act.” Gale has always disputed his firing, fought to get his job back and provided statements made by at least one of his superiors, saying some city leaders were out to get him.

On Wednesday, Gale’s attorneys filed a lawsuit in Federal Court in Colorado saying the city and O’Malley violated Gale’s First Amendment rights, finding a way to fire Gale in retaliation for his work with the Fraternal Order Of Police, a union representing sheriff’s deputies.

The 29-page complaint says the city and O’Malley “established an official policy or unofficial custom against disagreeing with or opposing them in administrative disciplinary proceedings, in public forums, or labor relations with employees.”

The complaint alleges the city and O’Malley went after Gale’s job, after he was outspoken on certain controversial issues, negotiated the deputies’ contract as part of his job with the FOP and organized a rally that would give sheriff’s deputies an avenue to speak on hot-button issues.

His firing centers around the treatment of a captain at the Sheriff’s Department implicated in a domestic violence situation. The captain had a previous relationship with then-Sheriff Gary Wilson. According to the federal complaint, Gale instructed that the captain shouldn’t be treated differently than other jail inmates, including having her change into prison garb. But according to legal documents, other law enforcement involved in taking the captain to and from jail for her court hearing bent the rules and Gale was blamed for it.

According to the federal complaint, no one else involved in the treatment of the captain at the jail or the courthouse has been disciplined.

The city of Denver provided 9NEWS a statement from Acting Deputy City Attorney Shaun Sullivan that read in part, “We have not been served a lawsuit filed by Mr. Gale. Once we receive it we will evaluate the claims and take appropriate action.”