SEOUL, South Korea — Overlooking the busiest intersection in Seoul is an 82-foot traffic camera tower. At the top is Kim Yong-hee, a 60-year-old man with a sleeping bag, plastic sheeting and placards denouncing Samsung, South Korea’s most powerful conglomerate.

He has been there for 315 days.

“Things can hardly get worse than here, but I am ready to fight Samsung in worse conditions,” Mr. Kim said by telephone from his midair protest camp, from which he can see the soaring towers of Samsung’s headquarters. “This is my last stand against that evil behemoth.”

Mr. Kim said Samsung fired him in 1995 for doing what many others, before and since, have tried to do: organize an independent labor union. He has spent the past quarter-century trying to get his job back, as well as compensation and an apology from the company, whose influence is so pervasive that many see it as untouchable.

Known around the world for its smartphones, Samsung is the biggest of the chaebol, the family-controlled conglomerates that dominate South Korea’s economy. And it stands out for another reason. Huge strikes have crippled operations at other chaebol, like the shipbuilding and automaking giant Hyundai, but Samsung has never experienced serious labor strife.