washington u.s. secretary state rex tillerson recuse issue relate transcanada corp application permit keystone xl pipeline state department say letter thursday environmental group greenpeace work matter department state play role deliberations ultimate resolution transcanada application say letter katherine mcmanus state department deputy legal adviser mcmanus letter come greenpeace write officials state department office government ethics wednesday urge tillerson recuse decisions multibillion-dollar pipeline give former role chief executive officer exxon mobil corp .. greenpeace argue letter exxon mobil would directly predictably benefit approval keystone xl firm investments canadian oil sand tillerson recuse matter early february mcmanus write transcanada try five years build 1,179-mile 1,897-km pipeline president barack obama reject 2015. transcanada resubmitted application keystone project january obama white house successor donald trump sign order smooth path line design link exist pipeline network canada unite state bring crude alberta north dakota refineries illinois en route gulf mexico exxon majority stake imperial oil calgary -alberta-based company operate kearl oil sand project northern alberta exxon mobil could benefit approval pipeline specific contract agreements transcanada either transport canadian tar sand production receive shipments u.s. refineries greenpeace write letter wednesday tillerson write january letter mcmanus one year resignation exxon mobil participate personally substantially particular matter involve specific party know exxon mobil party represent party unless first authorize participate also write case-by-case basis would recuse participation particular matter involve specific party determine reasonable person knowledge relevant facts would question impartiality matter unless first authorize participate tillerson recuse keystone pipeline issue state dept