Shipping companies represented by the Pacific Maritime Association are suspending the loading and unloading of vessels during four of the next five days as labor unrest at West Coast Ports continues.

In a statement released Wednesday, the PMA said the move was due to ongoing and costly slowdowns by dockworkers represented by the International Longshore and Warehouse Union along with premium-pay weekend and holiday dates. Yard, gate and rail operations will continue at terminal operators’ discretion. In Southern California, terminal operators will expand daytime vessel operations on non-holiday weekdays.

The four dates affected by the suspension of vessel operations are Feb. 12, Lincoln’s Birthday; the weekend, covering Feb. 14 and Feb. 15; along with Feb. 16, Washington’s Birthday/Presidents’ Day. The move follows the suspension of vessel operations last weekend.

Weekend and holiday pay rates command a premium of at least 50% of the basic longshore wage rate, according to PMA. The ILWU has denied workers have been engaged in a work slowdown and that freight at the ports is not backed up as the PMA claims.

“Last week, PMA made a comprehensive contract offer designed to bring these talks to conclusion,” said PMA spokesman Wade Gates. “The ILWU responded with demands they knew we could not meet, and continued slowdowns that will soon bring West Coast ports to gridlock. What they’re doing amounts to a strike with pay, and we will reduce the extent to which we pay premium rates for such a strike.”

Following negotiations that began last spring, the contract between the Pacific Maritime Association and the International Longshore and Warehouse Union expired on July 1. Despite nine months of ongoing talks, the lack of a contract and other operational issues has led to crisis-level congestion at the ports, including long wait times for truckers picking up or dropping off cargo containers. The delay in reaching a new agreement has lead to fears of a strike by longshoremen or a lockout of them by PMA members, either of which would likely shut down activity at West Coast ports.

PMA says while the ILWU has claimed that the parties are “this close,” to reaching a new contract agreement, it says they continue to push demands that would cripple the West Coast waterfront.

“The ILWU’s current slowdowns, now in their fourth month, show the very reason that we need a healthy arbitration system in place,” Gates said. “It is essential to be able to prevent the crippling slowdowns that are impacting workers and businesses across the nation.”

A federal mediator has been involved in the contract talks for about a month.

More than a dozen vessels are reportedly anchored off-shore at the Ports of Los Angeles and Long Beach. This and other delays at West Coast ports has resulted in some freight being shifted to other facilities with the National Retail Federation saying such diversions have already been more than it expected.