Boston City Councilor Ricardo Arroyo violated the state’s conflict of interest law by continuing to represent his brother in a 2018 civil lawsuit after he was first elected to the city council in 2019, the State Ethics Commission said in Tuesday statement.

Arroyo signed a document admitting to the violation and agreed to pay a $3,000 penalty.

The penalty follows a high profile sequence of events in which former U.S. Attorney Rachael Rollins  was accused of colluding with Arroyo to influence the race for Suffolk County District attorney, of which he was a candidate. Arroyo has denied he did anything wrong.

Rollins resigned her office earlier this year following a federal investigation.

The State Ethics Commission agreement did not describe the lawsuit in detail, only noting it was filed in Suffolk County Superior Court. A ethics commission spokesperson declined to dive into further detail, saying the commission could not “discuss matters that are outside of the content of the disposition agreement.”

Felix G. Arroyo, Ricardo Arroyo’s brother, was sued by Hilani Morales in 2018 and Ricardo Arroyo was listed as one of the three lawyers representing his older brother. Morales, a former city employee, accused Felix G. Arroyo of sexually harassing her and retaliating against her. Felix G. Arroyo denied the allegations.

The State Ethics Commission said Ricardo Arroyo did not serve as lead attorney for his brother in the unspecified lawsuit but “conducted and participated in several depositions.”

“At least three of the depositions [Ricardo] Arroyo conducted occurred after he was sworn into office as a Boston City Councilor,” the signed agreement with the State Ethics Commission said. “One of the depositions Arroyo conducted while serving as city councilor was of a city of Boston employee and another was of a city contractor.”

Zachary Lown, a lawyer for Ricardo Arroyo, said nothing Ricardo Arroyo did as an attorney on the lawsuit “negatively impacted the city or its interests, Arroyo’s client and the city are co-defendants, nor did the City ever express any concern to Councilor Arroyo about his legal representation.”

After Ricardo Arroyo was informed in August 2022 by the State Ethics Commission that his participation in the lawsuit might be a conflict of interest, he “immediately” began the process of withdrawing, Lown said.

“Councilor Arroyo then moved to withdraw before the next scheduled court date and five months prior to any finding by the State Ethics Commission,” Lown said in a statement. “We are grateful to the State Ethics Commission for working with us to resolve this matter.”

The ethics commission said it contacted Arroyo — first elected to the council in November 2019, sworn into office in January 2020, and re-elected in 2021 — on Aug. 18, 2022 and again several days later regarding his representation of his brother “and the concerns that representation raised under the conflict of interest law.”

State officials said Arroyo asked the lead attorney on the lawsuit to file a motion to withdraw on his behalf on Oct. 24, 2022 but it was not filed until Nov. 18, 2022. The motion was granted on Feb. 16.

State law prohibits municipal employees from acting as an attorney “for anyone other than the municipality in connection with any particular matter in which the municipality is a party or has a direct and substantial interest,” according to the state ethics commission.