With 40 employees and less than $5 million in annual revenue, the franchise hotel in SeaTac, Wash., could be the typical American small business. But the Holiday Inn Express will soon have to give most of its staff pay raises that are anything but routine.

Officials in SeaTac, which is 10 square miles nestled between Seattle and Tacoma and consists of an airport and its surroundings, confirmed this month that it will raise the minimum wage for many workers to $15 an hour starting in January. That's a 63% increase and the highest...