NEW YORK (CNN/Money) - Management at all West Coast ports have locked out dock workers, charging their union had coordinated work slowdowns at a number of ports.

The Pacific Maritime Association, which represents major shipping lines and port terminal operators, said the lockout started at 6 p.m. PT (9 p.m. ET) Friday as the evening shift was due to report to work, and that it would end the lockout 8 a.m. PT (11 a.m. ET) Sunday. It called on the International Longshore and Warehouse Union to halt the slowdowns, which management has referred to as union attempts to have "strikes with pay."

Both sides have scheduled a meeting for Saturday afternoon.

While a management source said the ports would reopen Sunday no matter the union response, he said that further lockouts were possible if the union did not cooperate.

Union officials continued to deny there was any slowdown at the ports, saying the union was moving record amounts of cargo. There are 10,500 ILWU members working at 29 West Coast ports.

"PMA's slanderous allegations of slowdowns during the biggest speedup in ILWU history that coincides with a record number of on-the-job deaths is literally adding insult to injury and making any progress toward a contract more difficult," said a statement Friday from ILWU International President James Spinosa. "Still the ILWU is prepared to go back to the table and seek a negotiated settlement."

A work stoppage has the potential to choke off trade between the United States and Asia and cost the U.S. economy as much as $1 billion a day. Saturday is a normal work day for the ports, which load and unload ships seven days a week. The dispute comes as ports are in the midst of the peak season to handle goods for the holiday shopping season. It is estimated by major retailers that every one-day delay at the port can back up goods for about a week.

The dispute between the ILWU and PMA has been simmering all summer and flared up in recent weeks.

Management has demanded that union agree to have data collected on other computers be downloaded into computers at the ports rather than entered by hand by ILWU-represented clerks. The maritime association says it has offered job guarantees for current clerks as well as improved pensions and pay as an inducement for the union to agree to the change.

For its part, the union says it has offered to allow greater use of technology but is demanding staffing level guarantees and jurisdiction for other work at the port, which management has refused to do.

"The PMA and (PMA CEO Joseph) Miniace are making false claims regarding an alleged work slowdown to cover the fact that they have refused to negotiate with the ILWU on a reasonable technology proposal," said a statement on the union Web site.

Earlier this month, management charged the union was not sending enough members to work for a key terminal operator at the Port of Long Beach, and threatened to lock out the union at the nation's busiest port complex -- Long Beach and Los Angeles -- unless it provided full staffing for all terminals. The union complied with the demand, averting the lockout at the eleventh hour.

On Wednesday management issued a statement saying the union had reached an agreement on the framework of a deal to incorporate new technology, but the union denied any accord. Union spokesman Steve Stallone said the agreement had only been with a negotiating subcommittee, not the union's full negotiating committee.

The union responded by posting a notice on its Web site calling on members to follow all safety procedures including speed limits and refraining from working extended shifts or working through lunch hours.

Management says those statements amounted to a call for a slowdown. It said Friday that work flows were far below average productivity levels, with dock workers moving between 3-to-12 containers of cargo an hour rather than the average of about 30. Stallone denied management claims Friday evening.

President Bush can intervene to order the two sides to return to work for an 80-day cooling-off period, although he lacks the power to help impose a settlement on the two sides that he does in the case of airline and railroad labor disputes. While many observers expect Bush to intervene if the dispute drags on, they did not expect him to intervene in the first days of a work stoppage.

The administration urged both sides to resolve the dispute, but said it would not intervene to keep the docks open.

"At this point, we are hopeful the two parties will come back to the bargaining table in good faith," Department of Labor spokeswoman Sue Hensley said. "We are monitoring this very

closely."