The union representing U.S. dockworkers has signaled that 45,000 members will walk off the job at midnight, kicking off a massive strike likely to shut down ports across the East and Gulf coasts.

A dockworkers' strike is set to shut down ports across much of the US indefinitely, threatening significant trade and economic disruption ahead of the presidential election and the busy holiday shopping season.

A lengthy shutdown could raise prices on goods around the country and potentially cause shortages and price increases at big and small retailers alike.