Union leaders rejected a sixth contract offer Royal Dutch Shell Plc made to U.S. refinery workers, and a pause in negotiations was called Thursday on the fifth day of a strike, though talks are set to resume next week. The United Steelworkers union (USW), which represents workers at 63 U.S. refineries, had recommended that locals reject the proposal, which was floated after the first big walkouts since 1980. “The parties have recessed and have agreed to resume talks,” Ray Fisher, spokesman for Shell whose U.S. unit leads negotiations for oil companies, said after the union rejection.