THE MBTA IS PREPARING to turn over its cash collection and money-counting operations to Brink’s Inc., the first major privatization move at the agency under special authorization granted by a 2015 state law.

Brian Shortsleeve, the T’s chief administrator and acting general manager, said contracting out the work to Brink’s will save the agency between $5.4 million and $8.2 million a year, depending on how the T’s costs are calculated. Shortsleeve said privatization would allow the T to avoid spending $1.2 million to modernize the agency’s existing money room and recoup $3.2 million by selling the existing money room facility and the agency’s armored trucks.

Shortsleeve said the T’s Fiscal Management and Control Board is expected to vote on hiring Brink’s on Thursday. He said he did not expect the board debate to take very long.

“We understand this is controversial. We understand that these sorts of changes are not easy,” Shortsleeve said. “But we are committed to doing what needs to be done to put the T on a path to fiscal sustainability.”

As Shortsleeve was briefing reporters on Wednesday in a conference room next to his office, officials from the Boston Carmen’s Union came in uninvited to the room to listen to his presentation. Afterward, they disputed some of Shortsleeve’s numbers and said existing federal law may require Brink’s to hire the affected T workers. T officials sharply disputed the union’s interpretation of federal law.

Shortsleeve said the money room employs a total of 72 people, seven of whom have already left their positions to take bus driver jobs at the agency. James O’Brien, the president of the Carmen’s Union, said Shortsleeve was overstating the number of employees. “My actual count is 47,” O’Brien said, adding that through retirements and people returning to bus-driver positions the number will drop to 33 in November.

Despite the new law exempting the MBTA from what are considered onerous privatization restrictions, O’Brien said his union will fight the effort to turn over money room jobs to outside contractors. “They’re our jobs. We’d like to continue doing that work,” O’Brien said.

The union chief said he and his coworkers crashed the press briefing because Shortsleeve has not shared information with them.  “This is not a transparent process,” he said. “It’s like this has already been decided. The way he makes it sound, this is going through tomorrow with no problem.”

Both sides were cordial during the press briefing, but both T and union officials are digging in. Last week, the T released a photo taken inside the money room in February that showed an employee face down on the floor, apparently taking a nap. The MBTA called the photo “troubling” and said “there is no logical reason for a transit system to be in the cash-handling business.”

O’Brien said the employee in the photo was a supervisor and not a member of the Carmen’s Union.

During his briefing, Shortsleeve said the T began looking for a private company to handle the agency’s money room operations and security in July. He said two companies made bids on the work, with Brink’s saying it could do the job for $3.6 million a year and Garda World submitting a price of $4.7 million. He said an evaluation committee of five MBTA managers selected Brink’s as the winning bid on Monday and the approval of the Fiscal Management and Control Board will be sought Thursday.

He said the potential savings from privatization depend on how existing costs are calculated. The current budget for money collection and security is $9 million, which consists of $5.8 million in labor costs, $2.2 million in health care and pension costs, and $1 million for materials and services. Shortsleeve said the long-term health care and pension costs are probably understated by $2.8 million, which would bring the T’s total cost to $11.8 million.

Shortsleeve said Brink’s is highly respected in the cash collection and transportation industry and would handle the T’s business with its own workers at its own facilities. He said the T would have full electronic oversight of the Brink’s operations. Any money lost or stolen would be covered by an insurance policy, he said.

The proposed contract is for two years with the option for three, one-year extensions. Shortsleeve said the short duration of the contract is important because the T hopes to move to a new fare collection system that would largely dispense with cash transactions. “Our goal long-term is to get out of the cash business,” he said.

Shortsleeve said there are 72 budgeted positions in the T’s money room and nearly all of the workers have enough seniority to take jobs driving buses. He said seven employees have already done so. He indicated the elimination of the 72 money room positions would yield large savings for the T even though none of the workers may actually leave the agency. He indicated the savings would arise because the agency will have to hire fewer new bus drivers.

O’Brien disputed those numbers, but acknowledged he and the union have had difficulty getting information from T managers. “They’re not being transparent on this,” he said. “The public deserves to know how their money is going to be spent and where it’s going to be spent.”

As for the savings promised by the T, O’Brien dismissed the figures, saying Brink’s submitted a low-ball bid and will hike its fees once it gets hired. When the T hired Keolis to run its commuter rail operations, that’s what happened, O’Brien said. “They’re here to make a profit on the back of taxpayers,” he said of Brink’s.