Negotiations over a new labor contract for West Coast dockworkers are under increasing strain as their employers say a failure to spread out lunch breaks has disrupted operations at the twin ports of Los Angeles and Long Beach since Wednesday.

Employers are allowed to stagger shifts around lunch times so there’s enough dockworkers available to deliver and receive containers, said the Pacific Maritime Association, which speaks for terminal operators and ocean carriers, in an emailed statement to Bloomberg on Monday. But “beginning last week, ILWU Local 13 has stopped complying with that contract provision,” the PMA said, referring to the local chapter of the International Longshore and Warehouse Union.

The statement is the most visible acknowledgment of a labor disruption since talks began last May, and it comes as cargo volumes drop sharply at the Southern California ports from peak levels a year ago. The threat of union unrest has spurred retailers, manufacturers and other importers to avoid potential shipping snarls by diverting goods to East and Gulf coast.

The PMA and the ILWU, which represents about 22,000 dockworkers on the West Coast, had pledged not to comment in the media and to continue working without issues such as slowdowns or lockouts. As recently as Feb. 23, they issued a joint statement saying they were hopeful they would reach a deal soon.

The PMA said the actions are causing “significant delays.” And, because the two sides have been operating without a contract since July 1, “there is no option for PMA to arbitrate the matter and require the union to man the terminals continuously without interruption.” 

Yusen Terminals LLC CEO Alan McCorkle said the actions haven’t caused much of an impact to his Port of Los Angeles terminal, but that the trucking community has been affected with long queues and delays.

Cargo movement by truck at the twin ports is now “completely shut down” from 12pm to 1pm daily, instead of normally running at about half-capacity over the meal time, “which causes a longer truck queue and delays to the trucking community,” McCorkle said.

ILWU President Willie Adams said in a statement his members are allowed “to take a lunch break just like everyone else.” The union said dockworkers are working every day, according to their agreements with the PMA, and that trucks can form lines for many reasons. The union said the PMA is using the lines to try to influence public opinion.