MKE Mitchell Airport passengers without masks to be 'denied boarding' MKE Mitchell Airport passengers without masks to be denied boarding Just before midnight Monday, Feb. 2, a new federal mask mandate takes effect for nearly all forms of transportation. MILWAUKEE - Just before midnight Monday, Feb. 2, a new federal mask mandate takes effect for nearly all forms of transportation. For nearly a year, Milwaukee County Transit System riders have been required to wear a facemask while on board. "The vast majority of people are complying with the mask requirement," said Matt Sliker, MCTS spokesman. Sliker said he hopes new orders from the U.S. Centers for Disease Control and Prevention will further enhance those efforts.