It’s not all kumbaya and kombucha at the Park Slope Food Coop — where life under its socialist-tinged grocery store is apparently so oppressive that the paid workers are trying to unionize.

Employees of the Brooklyn food collective recently alleged unfair labor practices by the co-op in a filing with the US National Labor Relations Board.

In response, the crunchy-granola collective’s iron-fisted management threatened and punished those who support the effort — with one union-busting boss telling workers they “should have a backup plan” if their collective bargaining doesn’t bear fruit, according to a copy of the labor complaint filed by the Retail, Wholesale and Department Store Union. The missive was obtained by The Post through a Freedom of Information Act request.

While a majority of the co-op’s roughly 17,000 members volunteer 2 ³/₄ hours a month for the privilege of buying the store’s low-cost, environmentally friendly fare, it’s the roughly 75 paid, full-time employees there who are digging in for a union fight.

Most of the employees were afraid to provide details of their union battle, telling The Post that they feared their bosses would crack down on them. But one source said the overworked employees are demanding more staffing, better scheduling practices and more transparency from co-op brass.

“Obviously, there’s something going on that’s not fair. I don’t want to say too much right now,” an employee told The Post.

“It’s like a pimple. If you don’t pop it, it just grows. We wouldn’t push it if something wasn’t hurting.”

Sources at the store said managers don’t want a union because that would prove the co-op isn’t the socialist paradise it purports to be.

The co-op — which a former member once described as “something between an earthy-crunchy health food haven and a Soviet-style reeducation camp” — is famous for its lefty politics.

Since its inception in 1973, the cooperative has at various times boycotted Coca-Cola, California grapes, Domino sugar and Williamsburg-based kosher food producer Flaum Appetizing Products — because of unfair labor practices.

Members also have been warring for a decade over whether to ban Isareli products to protest the occupation of Palestine.

The union-busting allegations are just its latest controversy.

Co-op administrators Joe Holtz and Ann Herpel incurred members’ ire in 2017 for dipping into the cooperative’s coffers to fund flights to Paris.

And in 2011, some more well-heeled, capitalistic members were busted paying their nannies to work their monthly volunteer shifts.

The Retail, Wholesale Department Store Workers Union confirmed it is helping co-op employees unionize.

Management did not return a request for comment.

Additional reporting by Ruth Weissmann and Shari Logan