The union representing U.S. dockworkers 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 possible strike by a union representing about 45,000 dockworkers could lead to a shutdown of U.S. ports from Maine to Texas starting Tuesday. Such a disruption could increase prices and cause shortages at retailers just as the holiday shopping season approaches.

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