U.S. retailers, bracing for a blow as they stock up for the crucial holiday sales season, asked the government to step in and help resolve a growing crisis caused by the near-collapse of South Korea’s Hanjin Shipping Co., one of the world’s largest container shipping companies.

“While the situation is still developing, the prospect of harm is significant and apparent,” Sandra Kennedy, president of the Retail Industry Leaders Association, wrote in a letter to the Department of Commerce and the Federal Maritime Commission. Hanjin’s...