As partygoers in sequins and tuxedos filed into the Museum of Modern Art’s annual gala, Grace Kwon stood across the street, wiping rain from her eyes and shouting along with her museum coworkers: “Modern art, ancient wages!”

Kwon, who works in visitor services at MoMA’s front desk, was one of approximately 100 unionized workers who gathered on Tuesday evening to protest against potential cuts to their healthcare plan. The protesting employees are members of Local 2110 of the United Auto Workers, a union of which this reporter was also a member from 2008 to 2011 through employment at the Village Voice.

The demonstration, which lasted two hours under steady showers, was timed to disrupt the Party in the Garden, MoMA’s black-tie fundraising soiree honoring the artists Richard Serra and Kara Walker. Tables at the dinner ranged from $25,000 to $100,000, and this year’s well-heeled attendees included Michael Bloomberg, Cindy Sherman and Chuck Close. Singer the Weeknd headlined the after-party – performing, somewhat ironically – his ballad Earned It.

Attendees at the MoMa Party in the Garden paid $25,000 to $100,000 for a table at the benefit. Photograph: Scott Rudd

“The museum needs to understand that their best resource is their staff,” said Kwon, 30, a member of the workers’ negotiating committee. She clutched a sheaf of neon orange flyers titled “We Are MoMA”, pressing them into pedestrians’ hands.

“They’re boasting about their their billion-dollar endowment, and tonight they’re going to raise millions. Yet they’re trying to shift the cost burden of healthcare on to us. It’s totally unacceptable.”

Sodden protesters hoisted signs reading “Put People First!” and “Last Year Matisse Cut-Outs. This Year: MoMa Health Care Cuts?” (a reference to a recent exhibition). They were most vocal against a proposed change to their healthcare plan that would requite higher premiums and raise copays up to 15% for hospitalizations and surgeries.

MoMa workers protest outside Party in the Garden benefit. Photograph: Stacey Anderson

Several huddled under black umbrellas with interior patterns of bright blue skies, a cheeky top seller from the MoMA gift shop.

Negotiations began in April between the workers’ union, which, despite its title, includes technical and office workers, and MoMA. The workers’ most recent collective bargaining agreement with the museum expired on 20 May, after which the union filed an extension that expires on 20 June.

Museum librarian David Senior, 39, made the protest into a family affair. He chanted, “Share the wealth, protect our health!” alongside his wife, Renee Smith, an artist. Their 22-month-old daughter, Isla, toyed with a blue-and-white union placard inside her stroller.

Smith, who is eight months pregnant, was grim about the proposed cuts. “If we have additional healthcare needs after the baby is born, we could be in debt indefinitely,” she said.

Local 2110 president Maida Rosenstein, 63, said the union counted 280 MoMA employees, including retail clerks, conservators and archivists. “They’re the people who make this museum work,” she argued.

Tuesday marked the first union protest at the MoMA since 2000, when Local 2110 members staged a 134-day walkout. The union has not set a strike deadline for current negotiations, and has scheduled a bargaining meeting today with the museum.

Tom Griesel, a collection photographer, called current issues “frighteningly similar” to those that prompted the 2000 strike.

“We struck over healthcare and here we are 15 years later, negotiating over healthcare,” said Griesel, 61. True to his work, he snapped photos of the protesters throughout the evening. “It’s a similar path we’re heading down. We’re hoping to avoid a strike, though.”

Low wages were also a source of contention.

MoMa librarian protests with his wife Renee Smith, who is eight months pregnant, and his daughter Isla. ‘After the baby is born, we could be in debt indefinitely,’ Smith says in regard to the healthcare cuts. Photograph: Stacey Anderson

“The average salary around the whole union is $49,000,” said Rosenstein. “No one expects to get rich working at the Museum of Modern Art, unless you’re one of the trustees.”

During the protest, the MoMA issued a statement: “The Museum of Modern Art has an outstanding staff. At this time, we are in the process of negotiations with Local 2110, and are optimistic that we will reach a positive outcome for the staff and all concerned.”

Most of the glamorous attendees did not acknowledge the chanting crowd across the street. However, a few at the gates were sympathetic. Harley Harris, an employee of the event company Staffing911, nodded to the demonstrators as he shielded guests with a large umbrella.

“It’s weird standing on this side,” said Harris, 20. “I feel like people are looking at me like I’m part of the problem, but I’m broke, too.”