FRANKFURT/NEW YORK (Reuters) – Deutsche Telekom (DTEGn.DE) is facing growing pressure from investors and lawmakers to ensure proper treatment of workers at its American business T-Mobile US (TMUS.O). The German company’s biggest subsidiary has enjoyed two years of rapid expansion in a fiercely competitive U.S. market that has seen it overtake its closest rival Sprint (S.N) in terms of subscribers. T-Mobile, which has about 45,000 employees, says it abides by the law and denies mistreating workers.