West Coast shipping companies today accused union longshoremen of a systematic, concerted work slowdown that was causing a "debilitating" backlog of container traffic at the ports and hurting the U.S. economy.

Spokesmen for the longshoremen's union vehemently denied the charges and said the workers were unloading the ships as fast as they safely could, and they blamed any slowness on mismanagement by the shipping companies.

Officials of the Pacific Maritime Association, which represents the shipping companies that operate at the West Coast ports, said that in the first week after the docks were reopened by a federal court order, the movement of the truck-sized metal containers slowed dramatically. In some ports, goods were moving 30 percent slower than normal. The PMA today forwarded its productivity data to the Justice Department to support its allegations. The union is expected to respond by Friday.

If evidence of a slowdown can be supported, the federal government could seek fines and contempt rulings from the judge who ordered both the shippers and longshoremen back to work.

Specifically, the PMA charged that the union had slowed container traffic into and out of the ports by 34 percent in Oakland; 29 percent in Portland; 27 percent in Seattle; 19 percent in Tacoma; and 9 percent in Los Angeles.

The shippers also charged that the union was purposefully supplying fewer workers than were needed, while others reported for work, only to leave, saying they were sick.

The union "is playing games with the U.S. economy and inflicting hardship on scores of companies and their employees," said PMA President Joseph Miniace. "Given the extreme urgency of keeping the goods moving through our ports, I cannot fathom why the union would deliberately take these slowdown actions."

Officials of the International Longshore and Warehouse Union, which represents about 10,500 dockworkers and clerks in 29 West Coast ports, said the charges of a deliberate slowdown are false and misleading.

"There's not one shred of evidence. They've just thrown out a bunch of numbers," said Steve Stallone, a spokesman for the ILWU.

"This is what we've been saying all along. They want to fine the union into bankruptcy and put our people in jail," Stallone said.

The union agreed that the containers had been moving more slowly through some ports, but Stallone blamed it on the backlog and chaos created by the PMA itself, which locked workers out of the ports for 10 days. Stallone said that at the best-run terminals, the containers were speeding through the ports. The ports were ordered reopened on Oct. 9 after the Bush administration used the broad powers of the Taft-Hartley Act to seek a court order requiring work at the docks to resume at a "normal and reasonable" speed.

The dockworkers say they are loading and unloading ships as fast as they safely can, but that the backlog has made an already hazardous job now even more dangerous. In support, five U.S. senators sent a letter to Labor Secretary Elaine L. Chao requesting that she assign federal inspectors to the ports to ensure safe working conditions.

Cargo is unloaded at the Port of Seattle on Oct. 10. Dockworkers say delays at some ports are due to the cargo backlog and shippers' mismanagement.Truckers await the reopening of the Port of Long Beach on Oct. 9, after a judge ordered an end to a 10-day lockout of dockworkers by the shipping companies.