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.

The International Longshoremen’s Association is demanding significantly higher wages and a total ban on the automation of cranes, gates and container-moving trucks that are used in the loading or unloading of freight at 36 U.S. ports. Those ports handle roughly half of the nations’ cargo from ships.