(Portland, OR)  --  TriMet is asking for a mediator in its negotiations on a new contract with Amalgamated Transit Union 757, which represents most TriMet employees.  TriMet Executive Director of Labor Relations and Human Resources Randy Stedman has sent a letter requesting the mediator to the state Employment Relations Board.  The two sides have been in contract talks for about five months.  One of the main points of contention is health-care costs for active employees and retirees.