By STEVE KARNOWSKIMINNEAPOLIS (AP) â¿¿ An American businessman who says he is being prevented from leaving Mongolia, where he is considered a potential witness in a corruption case, has asked for help from the congressional delegation in his home state of Minnesota. Justin Kapla is president and executive director of SouthGobi Sands LLC, a Mongolian mining company. He asked delegation members for assistance in lifting his travel ban, which he said was imposed because investigators consider him a witness in a corruption investigation of government officials involving the transfer of some of his company's minerals exploration licenses. In an email exchange with The Associated Press, Kapla declined to talk on the record. He referred questions to his father in Minnesota, William Kapla, who provided a copy of his son's letter to Sens. Al Franken and Amy Klobuchar and Rep. Michele Bachmann. "They're all working on it. All three of their offices are great," William Kapla, 72, of Forest Lake, said this week. He also said the U .S. Embassy has been talking to Mongolian officials. Justin Kapla, 39, wrote that the events in question happened well before he went to work for SouthGobi Sands. He said the Mongolian agency conducting the investigation, the Independent Authority Against Corruption, has acknowledged that but told him he still couldn't leave because it would need to hold someone responsible if the investigation finds any wrongdoing by the company. William Kapla told AP his son grew up in Elk River, is married to a Mongolian woman and has two children, all of whom are with him. He said his son is free to work and move around Mongolia but can't leave. "Would you want to sit in a country with an exit ban so you couldn't leave? What if an emergency happened at home?" William Kapla said.