The MBTA's largest labor union has agreed to a new contract which trades salary concessions for job security at an agency looking everywhere it can to cut costs and balance its budget.

Members of Boston's Carmen's Union, Local 589 ratified a three-year contract extension that cancels a scheduled 2.5 percent salary increase for bus drivers, subway operators and other workers next year and lowers their 2018 raise to 1.5 percent.

In return, the MBTA is guaranteeing that the Carmen's Union get to hold on to their jobs and maintain the current number of driving hours the MBTA provides.

"We're glad we were able to negotiate out of this privatization and it actually shows that through negotiations, instead of privatization, you can garner the same savings, if not more savings, than you would have had," Boston Carmen's Union, Local 589 president James O'Brien told reporters at MBTA headquarters Monday. 

The Carmen's Union is the MBTA's largest labor group and represents 4,100 T bus drivers, subway and trolley operators, maintenance workers, customer service agents, dispatchers and other workers. The contract with the Carmen's Union wasn't due to expire until 2018, but management and labor leaders said they negotiated the new extension over the past few months. The deal is expected to save the MBTA an average of $22 million a year over the next ten years.

The next contract also calls on the MBTA to give its workers a streamlined shift and route scheduling system that will give drivers more flexibility over when they work. The T will also begin a pilot program to allow drivers to work four 10-hour days instead of the current set of five eight-hour shifts. Part of the change includes the elimination of a paper-based scheduling system.

The new contract also slows the rate at which new MBTA operators move up the ranks into higher earning brackets.

If the re-worked hours were the carrot at the negotiations between acting MBTA General Manager Brian Shortsleeve and O'Brien, the stick was the looming threat that Baker's team would move to privatize operator jobs to cut costs. With that in mind, the drivers decided to defer their pay raises in order to save their positions.

Transportation Secretary Stephanie Pollack called the contract a "reset in labor/management relations for the MBTA."

"I think it is critically important for our overall goal of fixing the MBTA... because this will allow us to put behind us any issues of labor management disagreements with our largest union and go forward together to work to fix the T," Pollack said.

The union has been fighting a cold war of sorts with the Baker administration ever since Legislative Democrats granted Baker the authority to pursue privatization contracts without jumping through the usual approval hoops. Members of the union working in the MBTA's money-counting operation had their job eliminated earlier this year, with budget-minded T managers also looking at privatizing the workers who service the system's automated fare collection system. 

By reaching compromise with the T's top union over privatization, the Baker administration also avoids one of the only areas where Democrats have been willing to attack the popular moderate Republican governor.

O'Brien has been one of the staunchest voices against privatizing jobs at the MBTA.

The conflict between the union and Baker heated up in October when Baker's hand-picked MBTA Fiscal and Management Control Board voted to outsource the T's cash collection to the international firm Brinks with an $18.7 million contract. The Carmen's Union fired back at Baker after he said in an interview that the T-run "money room" couldn't account for some of the money it took in.

"Either Gov. Baker simply doesn’t know his facts, or worse, he is insulting employees," a spokesman for the union wrote at the time in response to Baker's claim.

Earlier in the month, O'Brien and six other Carmen's Union members were arrested outside the money room in Charlestown for unlawful assembly when they tried to stop vehicles from entering the facility during a demonstration.