Mayor Eric Adams met with union leaders — and was spotted ducking out of Gracie Mansion late Monday — despite his staff insisting that he’s too sick to maintain his usual jam-packed public schedule this week, The Post has learned.

Hizzoner’s SUV and security detail were spotted by The Post leaving the mayoral mansion at roughly 9:15 p.m. — and appeared to have been gone for several hours.

The vehicles hadn’t returned when a Post reporter left around midnight, but were spotted at roughly 6 a.m.

City Hall spokeswoman Kayla Mamelak contended to The Post that nothing was “weird” about the mayor’s late-night gallivanting, which unfolded after officials said Adams “hasn’t been feeling his best” and would clear his schedule as he undergoes medical tests.

But the trek and meetings with union leaders added another layer of intrigue to Adams’ purported illness and uncharacteristic absence from the public stage, especially as the mayoral primary looms and rumors abound that he’ll soon face new criminal charges.

The Post learned that Adams’ meetings with union leaders at Gracie Mansion — first reported by Politico — included a face-to-face with Rich Maroko, who leads the Hotel and Gaming Trades Council.

Adams told Maroko he’s running for re-election, to which Maroko responded, “If you’re in, we’re with you,” a spokesperson for the union said.

Adams also met with Manny Patreich, who heads the building service workers union 32BJ.

Patreich said the powwow covered the cost of living, local labor rights, housing affordability, “solidarity with immigrant workers and communities,” among other topics.

As far as an endorsement for Adams, Patreich said that would be up to the union’s board.

“The Board, composed of members and union executives, will then vote on who to endorse,” he said in a statement. “Our New York City mayoral endorsement process will begin in February.”

Both unions had backed Adams during the tight 2021 Democratic primary.

One political source said they believed Adams was gauging support ahead of an even-tougher 2025 primary in June, with his criminal case and potential pardon from President Trump looming.

“Union leaders put him in office,” a Democratic source said. “They are the people he believes he needs to inform of his plans, or to learn of their plans for him.

“Why in God’s name would you do that meeting if you were sick?” the source said. “You have to be lining something up. And if you are really sick, where are you going?”

City Hall officials didn’t return a request for comment on the union meeting.

– Additional reporting by Dorian Geiger