U.S. companies that rely on East and Gulf Coast seaports have been importing early, shifting goods to the West Coast, and even putting cargo on pricey flights to hedge against a threatened Oct. 1 strike that could jam supply chains and reignite inflation ahead of the U.S. presidential election.

"This is just another headache after everything else we've been dealing with," said Kenneth Sanchez, CEO of Chesapeake Specialty Products, which sends goods like metallic abrasives and foundry sand additives used to make engine blocks and transmissions to customers around the world.

His main port is in Baltimore, one of three dozen covered by an expiring contract between the International Longshoremen's Association (ILA) union representing 45,000 port workers and the United States Maritime Alliance employer group, whose renewal talks are at an impasse over pay.