With more than 12,000 locations around the globe, Dunkin' Donuts is one of the world's largest restaurant chains. The company recently expanded into California, opening up its first free-standing restaurants in the Bay Area and in Los Angeles. Now, the company is facing a trademark infringement claim. According to reporting from Reuters, the donut and coffee giant was recently sued by Heartland Consumer Products. Heartland makes Splenda, one of the country's most popular artificial sweeteners.