In California’s Napa Valley, the biggest concerns used to be the quality and quantity of the grape harvest and the traffic from thousands of weekend wine tasters.

But these days, a long-fermenting intellectual property conflict is bubbling over between producers of some of the Napa Valley’s high-end wines, the rest of the California wine industry and the Bureau of Alcohol, Tobacco and Firearms (BATF) involving something called “geographic brand names of viticultural significance.”