A federal mediator was expected to arrive in southern California on Tuesday to take part in negotiations over a new contract between employers at 29 U.S. West Coast ports and the union representing some 20,000 dock workers. Negotiators for employers and the union opened talks in May and agreed to keep talking after the old contract expired on June 30. The parties said in August they had reached a tentative deal on healthcare benefits but remained at odds over other issues ranging from wages to work rules. “We are pleased that the International Longshore and Warehouse Union and the Pacific Maritime Association have agreed to enter mediation. It’s in everyone’s best interest that goods keep flowing and people are working at our ports, which have a profound impact on our regional and national economies,” Los Angeles Mayor Eric Garcetti said in a joint statement with Long Beach Mayor Robert Garcia. “We all want a contract that’s fair to the industry, its workers, and the Ports of L.A. and Long Beach, and we are hopeful that the involvement of a federal mediator is the missing piece needed to get one signed,” Garcetti and Garcia said. Last month The Pacific Maritime Association asked the International Longshore and Warehouse Union in December to consent to federal mediation but the union balked, saying that talks were making slow but steady progress on their own. “We just didn’t think it was necessary (in December) but the union has never been rigid or fixed,” ILWU spokesman Craig Merrilees said. “If that’s going to move things forward then we’re pleased both parties made that decision.” Management sees an eventual settlement as key to easing severe cargo delays that began in mid-October at several container ports that account for nearly half of U.S. maritime trade and over 70 percent of imports from Asia. The congestion has been most pronounced at Los Angeles and Long Beach, the nation’s two busiest shipping hubs, which together handle 43 percent of all container cargo entering the United States.