Mayor Wu’s administration has reached a tentative labor agreement with Dorchester-based Firefighters Local 718. The agreement was reached Sunday night.

The agreement was announced at the Greater Boston Labor Council’s Labor Day breakfast, which drew hundreds of union members, and top Massachusetts elected officials and labor leaders, to the Boston Park Plaza hotel.

The details of the agreement were not immediately available. The agreement was reached at 10 p.m. Sunday, in the back room of the Brendan Behan Pub in Hyde Square, according to a City Hall source.

The union, which had previously clashed with the Wu administration over vaccine mandates and helped fund an outside group opposing Wu in the 2021 mayoral election, has roughly 1,600 members. The union is based out of Dorchester's Florian Hall.

In her speech to breakfast attendees, Wu noted that when she entered office in November 2021, 48 city union contracts had expired. Her administration committed to moving quickly to settle those contracts with wages and benefits the city's workforce deserves, she said.

"Last night, we took another major step toward delivering on that commitment," Wu said.

The tentative agreement with the firefighters union, once ratified by its members, would leave just the police unions as those without a contract.

"Pending ratification, this tentative agreement is the result of months of staying at the table together, bargaining focused on what our city needs, what our communities need, and what the brave individuals who keep them safe need, every day," Wu said. "This is also a testament to our administration’s unflagging focus on settling all of our contracts."

She said the practice of reacting to labor issues only when they come up should be left behind. Regarding the city's various union contracts, Wu said, "our administration will stay on top of them and do whatever it takes to never allow a contract to expire without another contract that’s ready to go."

Sam Dillon, the head of the union, spoke briefly on stage before the mayor, and quipped he was looking forward to her speech, “hanging on every word” she was going to say. He teed up the mayor's announcement, saying he expected to hear her demonstration of her "commitment to union workers."

The agreement still faces a ratification vote of the union.

Before the breakfast got underway, Wu and Dillon, both smiling, spoke with each other and clasped hands before going their separate ways in the ballroom. Wu's senior adviser for labor, Lou Mandarini III, stood off to the side.

In her speech, Wu gave a shoutout to Mandarini's father, Greater Boston Labor Council President Lou Mandarini II, who she said is enjoying a "well-earned retirement after more than 50 years with Laborers’ Local 22. Since before I started my political career in 2013, Lou has been a mentor, guide, and trusted adviser. I’ll miss you, Lou."

This story has been updated.