Massachusetts Bay Transportation Authority union workers and other labor supporters rallied outside the State House Monday as the Legislature prepared to hear testimony on the governor’s legislation to overhaul the embattled public transit agency.

Union leaders called on workers to flood the capitol to let legislators know about their opposition to the bill.

Steven A. Tolman, president of the Massachusetts AFL-CIO, told the rally the governor was attacking necessary protections for public workers. The bill calls for the suspension of the Pacheco law, which makes it difficult for public agencies to contract out services.

“They want to try and make this about the MBTA, but it’s about organized labor, in general,” he said.

Francis X. Callahan Jr., president of the of the Massachusetts Building Trades Council, also blasted the report that provided the roadmap for Governor Charlie Baker’s legislation. The report, assembled by a panel appointed by Baker, said the average T worker was absent 57 days of the year, but critics have questioned the validity of the number.

“They lied in that report,” Callahan said, noting that the figure included vacation days.

Baker proposed his legislation after the T faltered amid relentless snowstorms this winter, bringing the region to a standstill.

Among other changes, the bill also proposes a new oversight board for the T.

Both the Boston Carmen’s Union and the Massachusetts Republican Party called supporters to the public hearing on the bill in front of the Legislature’s Joint Transportation Committee.

Baker was expected to speak at the hearing, according to his administration.

Nicole Dungca can be reached atnicole.dungca@globe.com. Follow her on Twitter@ndungca.