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.

Dockworkers at ports from Maine to Texas began walking picket lines early Tuesday in a strike over wages and automation that could reignite inflation and cause shortages of goods if it goes on more than a few weeks.

The strike is impacting shipments of things like fresh food, cars and machinery. Our weekly “Econ Extra Credit” newsletter is an unexpected way to learn about the economy, one film at a time. Sign up to watch,