An arbitration board has overturned MARTA’s decision to outsource its paratransit service to a private company – a move the agency says could lead to poorer service at a higher cost.

MARTA decided to outsource its bus service for the disabled and elderly in 2015, citing the need to save money, increase efficiency and improve on-time performance rates. A private company – MV Transportation – has been operating the service since last spring.

But the Feb. 3 arbitrator’s decision gives the agency 100 days to bring the operation back in house. That means the agency will need to hire hundreds of bus drivers in coming weeks.

The decision is a victory for the Amalgamated Transit Union, which says MARTA’s decision to outsource the service violated the terms of its labor contract. Stanley Smalls, a union officer, said customers also will benefit from having experienced, well-paid drivers.

“It’s a victory for everybody that was affected by this outsourcing,” Smalls said.

In a written statement, MARTA said it is “reviewing the arbitrator’s decision before deciding next steps.” It could appeal the decision to Superior Court.

In the arbitration dispute, MARTA argued that “any effort to undo the contract with MV (Transportation) will adversely affect MARTA’s service to its most vulnerable customers.” It also argued the move would “have enormous and negative financial consequences.”

The arbitration board voted 2-1 in favor of the union. Among other things, it cited evidence that MARTA’s chief aim in outsourcing paratransit service was saving money on employee salaries and benefits – in essence, avoiding its obligations under the labor contract.