Some 45,000 union workers could walk off the job at seaports on the U.S. East and Gulf coasts on Oct. 1, cutting off vital trade arteries just weeks ahead of the nation's presidential election.

A J.P. Morgan analysis projected that a strike could cost the U.S. economy $5 billion daily.

The strike could hit 36 ports that handle about half of U.S. ocean imports. That could affect availability of a range of goods from bananas to clothing to cars shipped via container, while creating weekslong backlogs at ports. It could also stoke shipping cost increases that may be passed on to voters already frustrated with housing and food inflation, according to logistics experts.