SAN FRANCISCO/TOKYO (Reuters) – A labor dispute at ports on the U.S. West Coast is disrupting supply chains across the Pacific, forcing some Asian exporters to resort to costly air freight and pushing up shipping rates as more freighters are caught up in long lines to dock. With ports near gridlock and cargo delays being felt throughout the U.S. commercial supply chain, U.S. Labor Secretary Tom Perez plans to travel to San Francisco on Tuesday to help broker an agreement on a new contract between dockworkers and the group representing shippers and terminal operators.