A high-ranking Baltimore police union official who was reassigned to an overnight security detail in January after engaging in a series of arguments with local activists on Twitter has filed a federal lawsuit against the Baltimore Police Department and Commissioner Kevin Davis, alleging his reassignment and the department's social media policy governing officers' activities online are unconstitutional.

In the civil lawsuit, filed in U.S. District Court on Tuesday, Lt. Victor Gearhart — with the backing of the Fraternal Order of Police Lodge 3 — argues his reassignment was "retaliation against him for lawfully exercising his constitutional right to freedom of speech under the First Amendment," and calls the department's social media policy "overbroad, vague and otherwise unconstitutional."

The lawsuit says the actions taken against Gearhart, a 33-year veteran of the force and first vice president of the local FOP, have had a "chilling effect" on all officers' First Amendment rights, and that the policy represents illegal "prior restraint" on their speech.

Michael E. Davey, attorney for Gearhart and the FOP, declined to comment on Wednesday. T.J. Smith, a police spokesman, said he could not comment on pending litigation.

The lawsuit represents the first public backing of Gearhart by the union since the controversy surrounding his tweets first arose. The union has previously sought to distance itself from Gearhart.

Gearhart, known for his outspoken commentary on issues affecting Baltimore, first came under fire in January after officer-turned-reform-activist Michael A. Wood Jr. pointed out Gearhart's Twitter handle, @SDGhostRider, and youth activist Makayla Gilliam-Price wrote an article on the website Assata's Syllabus that provided examples of some of Gearhart's tweets to underscore her opinion that they "prove embedded racism" in the Baltimore police department.

On protests in the city, Gearhart wrote in December, "THUGS always act like THUGS" and "demonstrators act like animals." He also suggested that both State's Attorney Marilyn J. Mosby, who brought charges against six Baltimore police officers in the death of 25-year-old Freddie Gray from injuries suffered in police custody, and her husband, City Councilman Nick Mosby, should be "deported" from the country.

After Gilliam-Price's piece was posted, Gearhart engaged in a back-and-forth argument with her and other activists. Police officials deemed his comments a personal attack on Gilliam-Price, 17 at the time, and generally inappropriate — especially as the department hopes to repair its relationship with the community following the unrest after Gray's death. Both Davis and the FOP disavowed his actions, with the FOP tweeting, "Be advised: the statements made by @SDGhostRider do not represent or reflect the opinion or beliefs of our organization."

Davis then reassigned Gearhart, a Southern District shift commander, to an overnight security detail at police headquarters.

In November, the Baltimore Police Department instituted a five-page social media policy, which prohibits members from posting on their personal social media pages "any discriminatory, gratuitously violent or similarly inappropriate written content, audio files, photographs, or other depictions that are contrary to the mission and effectiveness of the BPD."

Such content, the policy states, would include any "racist, sexist or other discriminatory content that expresses bias against any race, religion, or other protected class of individuals," as well as any content "that might lead a reasonable member of the public to question whether the member is committed to constitutional, non-discriminatory policing."

Gearhart has said he never claimed to be speaking on behalf of the department in his tweets — actually pointing out that he wasn't speaking for the department — and that his reassignment was baseless and illegal.

In the lawsuit, he asks for unspecified damages and to be reinstated to his former post. He and the FOP ask that the court find the department's social media policy unconstitutional.