BÉZIERS, France — On a late evening in March, a group of winegrowers wearing black balaclavas forced their way into one of France’s largest wine brokerages and ignited three Molotov cocktails. Within minutes, the business, Passerieux Vergnes Diffusion, was in flames.

Vigilante vignerons had previously raided two big wine distributors nearby, in the Languedoc wine-producing region, smashing offices and dumping a river of red wine into the streets.

The businesses had one thing in common: They had struck deals to import inexpensive wine from Spain, prompting a backlash among local winemakers who feared their livelihoods were under attack.

“I was stupefied,” said René Vergnes, a native of Languedoc who has run the Passerieux Vergnes wine brokerage business for 35 years. “Everything was destroyed.”