In this April 24, 2015, file photo, riders board a "T" trolley car in Boston. Credit: Bill Sikes | AP

QUINCY, Massachusetts — Union workers protested the potential for privatization of labor at the Massachusetts Bay Transportation Authority.

Dozens of members of the International Association of Machinists and the Boston Carmen’s Union demonstrated in Quincy on Sunday to express outrage at the agency’s exploration of using an outside vendor, The Patriot Ledger reports.

“Privatization does not work at the MBTA or any public transportation, period,” said Jim Evers, president of the Boston Carmen’s Union. “If the MBTA decides to go this route, we’re going to fight and we consider this an attack on labor. The riding public does not deserve that.”

The agency floated the idea of working with an outside vendor to operate and maintain 60 buses in January, which led to tensions between union leaders and elected officials.

Joe Pesaturo, an MBTA spokesman, said in an email Sunday that the agency has a responsibility to find the most efficient way to serve riders.

But some critics of the potential plan believe privatization in some areas of the agency could creep into other areas of its service.

Workers protesting the proposed plan were joined by union leaders and Rep. Joe Kennedy III.

“The way that privatization works, off a system that wasn’t actually designed to make a profit, is you have to either cut from workers, or cut it from services, and one way or the other, people are going to lose,” Kennedy said.

Sen. Elizabeth Warren also sent a letter to MBTA General Manager Steve Poftak last month, expressing opposition to privatization, calling it a “misguided and short-sighted idea.”