Delta will begin daily service between Seattle and Philadelphia on May 7. It's the latest competitive flashpoint for Seattle hub carriers Delta and Alaska Airlines.
Alaska flies Seattle-Philadelphia up to four times per day. American, which operates a hub in Philadelphia, also flies the route at varying frequency -- up to four times per day in August but less than daily in January and February.
Delta said the new service will appeal to business flyers.
"Philadelphia has been a top-requested destination from our Seattle corporate customers, and this new service reflects our commitment to investing in the routes that matter most to them while building an even stronger network from the Pacific Northwest," said vice president of network planning Amy Martin.