More than 1,000 longshoremen have walked off the job at ports in New York and New Jersey, putting ship unloading at a standstill.
The walkout began at about 11 a.m. Friday. It wasn't immediately clear what prompted the action.
No ships were being unloaded and no trucks were being allowed to enter the port.
The Port Authority of New York and New Jersey is the ports' operator. It is working to get trucks that were in the port at the time out of the area.
Spokespeople for the International Longshoremen's Association and the New York Shipping Association didn't immediately respond to messages seeking information.
The New York-New Jersey port is the busiest port on the East Coast and the second-busiest in the country, behind Los Angeles/Long Beach, California.