The U.S. Postal Service is considering shutting down a large mail-handling facility in northwest Iowa, a move that would cut 140 jobs. About a hundred concerned citizens turned out at Sioux City’s city hall last night to listen to postal worker union officials explain the impact of the potential loss of a mail processing and distribution center in Sioux City. A union leader says the loss would result in increased delivery time and the loss of the city’s postmark, which could have an economic impact.