Nike Inc. doesn’t have enough sneakers to sell for the holidays. Costco Wholesale Corp. is reimposing limits on paper towel purchases. Prices for artificial Christmas trees have jumped 25% this season.

Despite mounting shipping delays and cargo backlogs, the busiest U.S. port complex shuts its gates for hours on most days and remains closed on Sundays. Meanwhile, major ports in Asia and Europe have operated round-the-clock for years.

“With the current work schedule you have two big ports operating at 60%-70% of their capacity,” said Uffe Ostergaard, president of the North America region for German boxship operator Hapag-Lloyd AG . “That’s a huge operational disadvantage.”

The American supply chain has so far failed to adapt to the crush of imports as businesses rush to restock pandemic-depleted inventories. Tens of thousands of containers are stuck at the ports of Los Angeles and Long Beach, Calif., the two West Coast gateways that move more than a quarter of all American imports. More than 60 ships are lined up to dock, with waiting times stretching to three weeks.

Waiting BoxesAverage days “dwell time” containers waitedon docks each month for handling at the portsof Los Angeles and Long BeachMonthly averageSource: Pacific Merchant Shipping Association
Jun-20Oct-20Feb-21Aug-210123456days

The ports of Los Angeles and Long Beach are managed separately and operate 13 private container terminals. Long Beach officials said last week they would try operating 24 hours a day from Monday to Thursday. Gene Seroka, executive director of the larger Port of Los Angeles, said his port will step more cautiously, keeping existing hours while waiting for truckers and warehouse operators to extend their hours.

“It has been nearly impossible to get everyone on the same page towards 24/7 operations,” Mr. Seroka said.

Truck drivers often don’t show up at scheduled appointments to pick up boxes at the inundated container yards to make space for the next load to come in, say shipping and port executives. Truckers blame terminal congestion, saying delays at one appointment can cause them to miss the next, and that shipping lines aren’t doing enough to clear out the towers of empty containers taking up space at the docks.

Before any changes this coming week, the longshore routine at the ports involve two shifts: 8 a.m. to 4 p.m. and 6 p.m. to 3 a.m. An overnight shift of five hours is available, but it is up to 50% more expensive and rarely used, say liner and terminal operators who foot the bill. Cargo pickups on Saturday are also rare, being charged as premium shifts, and there is no work on Sundays.

The International Longshore and Warehouse Union, which represents the dockworkers, said its members would work a third shift or on weekends, but the pileup of containers must first b