Can the rules change in the middle of the game? No—sort of. The US and Colorado Constitutions’ Contract Clauses prevent subsequent legislatures from impairing a public contractual obligation created by prior laws. This case involves the Colorado Public Employees’ Retirement Association (PERA), and the benefits it provides to government employee retirees; specifically, the cost of living increases (COLA) to PERA benefits. The court of appeals, reversing the trial court in part, held that government employees have a constitutional contractual right to the COLA rates set by statute at the time their rights to PERA benefits vested. But, such rights are violated only if they are substantially impaired, and there was no reasonable, necessary or legitimate public purpose for changing the rates. Those issues were returned to the trial court for further proceedings.