More than 4,200 nurses, support staff, maintenance workers and clerical employees at the five Mercy Health Partners hospitals in Greater Cincinnati will vote on whether to unionize. In a deal with the Service Employees International Union, Mercy and its parent company have agreed not to try to influence employee voting. If employees choose a union, they will start negotiating a contract. If they reject a union, the SEIU has agreed not to campaign at Mercy hospitals for three years.