The merger of Atlanta-based Atlantic Southeast Airlines and Houston-based ExpressJet hit another milestone Wednesday when flight attendants from the two regional carriers voted to be represented by the International Association of Machinists, a key step toward combining employee groups.

The Machinists union already represented the flight attendants from ExpressJet, and now takes over representation of the flight attendants from Atlantic Southeast as well. The Atlantic Southeast flight attendants had been represented by the Association of Flight Attendants. Each union had represented more than 1,000 flight attendants at their respective carriers.

In the election to represent more than 2,100 flight attendants, the Machinists union received 1,065 votes, while the Association of Flight Attendants received 666 votes, according to the National Mediation Board, which governs airline labor relations. There were 26 votes cast for no union.

The Machinists union said it is starting negotiations for a single contract for the combined group of flight attendants.

Meanwhile, pilots are also negotiating for a combined labor contract and have reached several tentative agreements.

Atlantic Southeast parent SkyWest announced the acquisition of ExpressJet last year in a deal with a cash value of $133 million.

The combined airline is based in Atlanta near Hartsfield-Jackson International Airport and will be the largest regional airline in the world, according to the company.

Starting Dec. 31, the combined airline will be called ExpressJet, bringing an end to the Atlantic Southeast Airlines name. Atlantic Southeast operates as Delta Connection and United Express, while ExpressJet operates as Continental Express and United Express.