Thousands of unionized dockworkers on the East and Gulf Coasts could go on strike as early as Tuesday, stranding cargo and sending ripples through supply chains for consumer goods and manufacturing parts.

A contract between the operators of port terminals and the International Longshoremen’s Association, covering workers who load and unload cargo ships at three dozen ports, is set to expire on Monday. Their facilities include massive container ports in New Jersey, Virginia, Georgia and Texas, as well as the Port of Baltimore, a major hub for the import and export of vehicles and heavy machinery.

The port operators group, the United States Maritime Alliance, and the union remain at an impasse over wage increases. Federal officials have said President Biden is not planning to invoke a nearly 80-year-old law to force dockworkers back to work if they strike. It would be the first such walkout at all these ports since 1977.

Which ports and goods would be affected?

Workers at ports from Maine to Texas would walk off the job at 12:01 a.m. Tuesday. These ports handle about half of all goods shipped to the United States in containers. One of them, the Port of New York and New Jersey, is the third busiest in the country.

Longshoremen play a crucial role in the movement of cargo. They are responsible for loading and unloading ships, and they secure vessels that arrive and depart from U.S. ports. For the most part, ocean transport to and from these ports can’t happen without them.

Cargo that could be affected by the strike includes everyday consumer goods, like bananas, many of which come through a port in Delaware. Just over half of imported apparel, footwear and accessories also come through East Coast ports. Manufacturing parts and cars move through these ports, too.