Maryland Lt. Gov. Anthony G. Brown (D) is set to pick up the endorsement Tuesday of a key state employees union, adding to the labor support of his 2014 gubernatorial bid.

AFSCME Maryland Council 3, which represents about 25,000 state employees and public university employees, plans to announce its backing of Brown at a news conference at noon in Baltimore.

Brown faces Attorney General Douglas F. Gansler (D) and Del. Heather R. Mizeur (D-Montgomery) in the Democratic primary for governor in June.

Brown has dominated the endorsement process to this stage of the race, winning the backing of many big-name Democrats as well as most of the liberal interest groups, including labor unions, that traditionally play a role in the election.

The Maryland-D.C. AFL-CIO Council, the umbrella group for labor in the state, announced its backing of Brown last month.