An independent arbitrator is ordering Massachusetts State Police to reinstate seven troopers who refused to be vaccinated for COVID-19. They were subsequently placed on unpaid leave. The decision means those troopers can choose to return to work with retroactive pay. The union representing troopers filed a grievance over former Gov. Charlie Baker imposing a vaccine requirement for all executive department employees in 2021. Current Gov. Maura Healey lifted the vaccine mandate in May after the public health emergency ended. The arbitrator concluded Friday that State Police violated a collective bargaining agreement in handling the cases.