The union representing customer service agents, reservations agents and baggage handlers at Southwest Airlines and AirTran Airways has reached a deal to combine work forces between the two carriers.

It’s the final major work group at Southwest and AirTran to reach such a deal.

The International Association of Machinists — which represents customer service, reservations and ramp agents at both airlines — outlined how the employee seniority lists will be combined and announced a deal with the company on the process for AirTran employees to transition to Southwest. The machinists union represents about 6,000 employees from Southwest and 1,700 from AirTran.

Some AirTran workers at airports where the carrier operates will begin transitioning to Southwest next month. The transition agreement outlines a plan for AirTran customer service agents to complete their transition to Southwest by Dec. 31, 2013.

The transition for employees comes as Southwest begins converting AirTran operations to Southwest in airports around the country.