Hundreds of MBTA workers wearing bright orange T-shirts that read “Keep Public Transportation Public!!!!! Stop MBTA Privatization” and chanting “We didn’t break the T!” rallied at the State Transportation Building on Monday to protest the possible privatization of bus driver and maintenance worker jobs.

The Boston Carmen’s Union Local 589, the T’s largest labor group, organized the rally at 10 Park Plaza to voice opposition against a recent report issued by the MBTA’s Fiscal and Management Control Board that said it could outsource bus operator and maintenance positions.

“By being here today, you are putting a face on this issue,” state Sen. Marc Pacheco said to the crowd. “You’re showing people the people who have the potential of losing their jobs.”

The possible privatization of bus operators and maintenance workers could affect hundreds of jobs. There are 450 bus maintenance workers and 1,700 full- and part-time bus drivers with the MBTA, according to The Boston Globe. The move could be the largest privatization effort by Gov. Charlie Baker’s administration.

“We’ve been down this road before, and privatization of public services is not the answer,” Pacheco said.

Privately contracted work is meant to save taxpayer dollars and may lower the cost of labor contracts, but there are hidden expenses, he said.

“You have the cost of the contract, and then you have to add to that the cost of unemployment, the cost of healthcare, the cost of housing,” Pacheco said. “When you factor that all in, where’s the savings?”

To union members, the rally wasn’t only about protecting the jobs threatened by current proposals, but to ensure that privatization doesn’t affect more areas within the MBTA.

“It’s like a crack in a damn,” said Allen Lee, a Carmen’s Union executive board member. “If we give [Baker] a little bit, he’s going to want to take a lot. It’s a threat, you can see it coming.”

A spokesperson for MassDOT said in an email that, “The MBTA’s focus is on delivering reliable service to our riders at a sustainable price and whether it’s done publicly or privately should not be the issue.”

Last month, the MBTA said that “everything was on the table” in terms of cost-saving measures in the face of a $32 million drop in projected sales tax revenue.

“As we seek to close what's a $100-plus million deficit this year, everything's on the table. Seventy-five percent of our costs are wages and benefits so that's a core area of focus for us," MBTA Chief Administrator Brian Shortsleeve told reporters then.

Boston Carmen’s Union executive board member Larry Kelly, who started the “We didn’t break the T” chant, said that the MBTA’s fiscal issues go above these individual employees.

“We don’t need praise, we all know who does the job,” he said. “You can’t blame us for the [MBTA’s] problems just like you don’t blame a weatherman for the weather.”

Monday’s event was the first of many rallies that the Boston Carmen’s Union has planned for this fall. There are 14 more planned from now until early November. Union officials urged workers to come to the upcoming rallies in larger numbers and with louder voices.

“The T has been mismanaged for years and the government wants to fix its financial woes on the backs of its workers,” said Lou Antonellis, president of the IBEW Local 103 union. “These careers at the MBTA are a pathway out of poverty and the jobs are going to go away if we don’t fight for them.”