Lovers of Champagne and other French sparkling wines should brace for big cost increases if the United States makes good on a threat to impose 100% tariffs on French goods in a dispute over the country’s planned digital services tax. A $70 bottle of Moet & Chandon Grand Vintage could surge to $130, for example, said David Parker, chief executive of Benchmark Wine Group, the largest U.S. supplier of fine and rare wines for wine retailers. The U.S. government said in December it may slap duties of up to 100% on $2.4 billion in imports from France of Champagne, handbags,...