First are the show of buttons.

Many employees aligned with the Glenstone Museum Workers United (GMWU) cause wear a button with a clock on it, drawing on a piece currently hanging in the museum by Felix Gonzalez-Torres. Management has proffered an alternative button, a yellow heart that reads “Glenstone Gives.” Some employees wear both.

Hourly workers are voting Thursday and Friday whether to join the International Brotherhood of Teamsters. Union supporters say that they want a living wage and better working conditions for roughly 100 eligible employees, including guides and staff from housekeeping, grounds, maintenance and food service — about half of the museum’s workforce.

Behind the scenes, the labor showdown at Glenstone involves more than uniform flair. Mitchell and Emily Wei Rales — the museum’s billionaire founders, whose home lies just across a pond — have taken a personal hand in trying to stop its workers from organizing, hiring a law firm and consultants and scheduling one-on-one sit-downs with staff.

“It is our sincere hope that you give due consideration to voting NO and keeping the Teamsters out of this special place we’ve built together,” reads a June 3 letter signed by the Raleses, delivered to workers’ doors this week via FedEx.

“Glenstone respects the right of its associates to decide whether to unionize,” the museum said in a statement. “In keeping with our core values of emphasizing direct engagement, embracing diverse perspectives, and supporting teamwork, our focus leading up to the election has been to ensure that all associates, not just some, can express their views and have access to factual information, not just materials supplied by the Teamsters.”

If museum staffers vote yes, Glenstone will join a wave of major museums whose employees — often highly educated and hourly paid — have unionized over the past few years, including the Art Institute of Chicago, Museum of Contemporary Art in Los Angeles and Whitney Museum of American Art in New York.

But in many ways Glenstone stands apart from its peers. Instead of offering docent tours, lengthy wall text or audio aids, the museum posts knowledgeable people in every gallery to help explain contemporary artworks. Glenstone’s vast grounds mean these visitor-experience shifts take workers outdoors, sometimes in bracing weather. The museum’s location in Potomac, an affluent enclave whose median household income was $218,710 in 2022, offers few housing opportunities nearby for hourly workers, organizers say.

And then there’s the museum’s extraordinary resources. The Glenstone Foundation reported net assets of $4.4 billion in 2022, on par with the mammoth Metropolitan Museum of Art. “The Met has around 2,000 employees,” says Elizabeth Shaw, grounds and visitor experience liaison for Glenstone and a union organizer. “We have 200.”

Visitor experience makes up the largest department at Glenstone. Stationed both inside and outdoors, the guides are identifiable by their gray uniforms, provided by the museum.

Organizers say outdoor shifts can be punishing for workers. Some employees say during winter, parkas provided by Glenstone aren’t warm enough for guides assigned to post up outside. Summer is worse, especially for staff asked to stand by Michael Heizer’s “Collapse” (1967/2016), a giant pit filled with steel beams that absorb and radiate heat.

According to a copy of Glenstone’s weather safety policy shared with The Post, the museum closes “Collapse” and other outdoor installations when the heat index exceeds National Weather Service thresholds of 105 degrees for two hours or wind chill of -18 degrees for one hour. At less extreme temperatures staff are advised to rotate posts and take other precautions.

Wages are another top concern for the organizers. Many Glenstone employees have second jobs, such as driving for delivery apps or bartending. One full-time associate pulls shifts at an Amazon warehouse, for example, while a part-time worker splits her time between Glenstone and the National Portrait Gallery. Part-time workers say they would love to get full-time hours to receive health-care benefits.

Glenstone has committed to paying 20 percent over the minimum wage of Montgomery County, which is currently $16.70 for large employers. But ahead of a stepped increase to the county minimum wage, the museum changed its policy. On May 8 — the same day that GMWU asked the leadership to voluntarily recognize the union — the museum told staff in a presentation that market-based wage increases would be merit based going forward.

“You shouldn’t have to have a side job in order to sustain yourself,” says Hannah Cianci, a guide who recently left Glenstone. “We’ll terraform a hill if an artist wants us to. We spare no expense when it comes to visitor experience. Workers are part of that.”

Glenstone hired the elite law firm Proskauer Rose to prepare for the election and has turned to Jim Monica of the American Labor Group, a consultancy that offers “union avoidance” services. Monica has hosted small-group meetings that some employees describe as both heated and misleading. One email from management shared with The Post described a session as a “National Labor Relations Board (NLRB) Training,” even though the federal agency played no part in it. (Monica did not respond to a request for comment.)

Beyond disseminating talking points, the Raleses have contacted employees directly, attending departmental meetings and putting holds on workers’ calendars. “It’s not like you have to go,” Cianci says, “but the founder of your workplace has scheduled you for a meeting.”

“We contacted all the associates — many of whom had not been included in the organizing drive — to provide strictly factual material,” said Glenstone in the statement, “and we brought in field experts with experience on both the labor and management side so we could offer publicly verifiable facts about labor and unions to anyone who wanted them.”

One staff session on May 30 brought the art-labor conversation full circle. The meeting in a museum loading dock touched on the work of Rirkrit Tiravanija, a social practice artist whom the GMWU cited in its first letter to leadership. Back in 2019, Glenstone hosted a project by Tiravanija, “Fear Eats the Soul,” in which the artist worked alongside hourly wage workers to serve food — pork that was slow-roasted in a pit built by a museum staffer, for example.

That performance piece positioned art museums as a platform for thinking about labor.

Chalk up Tiravanija’s work as another thing management and labor disagree over. Director Emily Wei Rales pointed to that project as a powerful demonstration of the museum’s core values, according to Shaw, but a cafe worker responded that for them, it also meant arriving early and staying late.