Another seat has opened up on the Cannabis Control Commission.

Ava Callendar Concepcion, who has been on leave for months, resigned from the commission, Attorney General Andrea Campbell’s office announced late Monday.

“Commissioner Concepcion has dedicated her career to social justice and brought a wealth of experience in public safety, equity and opportunity to her nearly five years on the Cannabis Control Commission,” Campbell said in a statement.

Concepcion was appointed to the commission’s public safety seat in January 2021.

“During her service in the public safety seat, Commissioner Ava Callender Concepcion played a key role in some of the most consequential changes to cannabis policy and regulation in Massachusetts, including the implementation of the state’s equity reform law, elimination of the two-agent rule for small delivery businesses, and increased employment opportunities for people who have been harmed by the war on drugs,” Neal McNamara, spokesperson for the commission, said in a statement.

It was not clear why Concepcion resigned. The CCC had been operating with three members for months, and unanimous 3-0 votes are needed to advance proposals with a three-member commission.

Concepcion’s resignation comes days after commissioners announced Carrie Benedon is joining the panel, which will bring it to four active members. Benedon works in Campbell’s office as director of the Division of Open Government and will fill the seat vacated by Nurys Camargo, who resigned in May.

Commissioners are aiming to vote on regulations governing social consumption sites by Christmas.

The commission’s next meeting is Tuesday.