The congestion is the latest bottleneck in supply chains that have been knocked off balance this year by container shortages, tight capacity and events such as the grounding of the Ever Given container ship in the Suez Canal in March, backups at the Yantian port in Shenzhen, China, and other incidents that led to ongoing delivery delays.

In Chicago, the freight railroads are trying to catch up as containers arrive faster than they can be switched for onward transport, leading to ever-higher stacks of boxes at the region’s yards. The strains are being exacerbated by labor and equipment shortages across the shipping, trucking and rail industries.

Union Pacific, which along with BNSF hauls containers to and from the Southern California ports, earlier this month said it would suspend service from the West Coast to Chicago beginning the night of July 18 for up to seven days to ease the backlog of containers.