It took a powerful union to get Mayor Bill de Blasio and Gov. Andrew Cuomo to attend the same event Wednesday — even if they couldn’t bear to stand on stage together.

The constantly feuding pols spoke to thousands of workers from the Service Employees International Union Local 32BJ at a massive rally for a new contract.

Cuomo told the horde, stretching for blocks from East 82nd Street and Park Avenue, that they have “two allies who stand with you,” but noted that one of those allies were “each other.”

“Your other ally is me,” the governor said, pointing out he is a native of the city. “I am a born-and-raised New Yorker. I am coming to stand with you shoulder-to-shoulder 100 percent in this fight.”

Cuomo then left the stage while greeting Public Advocate Letitia James, Comptroller Scott Stringer and various union members.

De Blasio was nowhere in sight until he hopped onto the stage about 10 minutes later and flaunted his credentials.

“I want to introduce myself formally. My name is Bill de Blasio and I am mayor of the biggest union town in the United States of America,” he said.

“The reason we are all gathered here is about fairness. It’s not just about a contract; it’s about what a contract means.”

About 35,000 porters, doormen, superintendents and other union members who service about 3,500 buildings were bracing for a possible strike when their contract expires on April 20.

Cuomo and de Blasio — who have been publicly battling over public housing, mass-transit improvements and a host of other issues — appear together only when they have to.

The rally was one of those must-attend events.

That’s because SEIU 32BJ and its president, Hector Figueroa, wield enormous influence over Albany and City Hall.

“The group’s political clout and — more importantly — diverse membership of core Democratic voters make them a must-have ally for both men,” said Democratic political consultant Evan Thies.

The union is a longtime political supporter of de Blasio and Cuomo, who both got behind its campaign to boost the minimum wage to $15 an hour by 2019.

32BJ and its affiliates have given nearly $100,000 to Cuomo’s gubernatorial campaigns over the past decade.

De Blasio got a maximum-allowable $4,950 donation during last year’s mayoral race.

Besides appearing with de Blasio at various events, Figueroa scored seven meetings or phone calls with Hizzoner during the mayor’s first four-year term — including four in 2017, records show.