By Lisa Baertlein LAS VEGAS, Aug 26 (Reuters) - Package carrier FedEx Corp FDX.N is facing a threat from an unusual source - one of its biggest delivery contractors. Tennessee businessman Spencer Patton has ratcheted up pressure on FedEx to boost compensation for contractors after company actions made it even harder for them to wring out profit in a downshifting, inflationary economy. Memphis-based FedEx has traditionally been anti-union, but if Patton's efforts gain traction, they could squeeze the company's profit and disrupt business ahead of the crucial holiday shipping season.