Some states exempt non investor-owned utilities from some aspects of deregulation such as customer choice of supplier. For example, some of the New England states exempt municipal lighting plants from several aspects of deregulation and these municipal utilities do not have to allow customers to purchase from competitive suppliers. Municipal utilities in these states can also opt to function as vertically-integrated utilities and operate generation assets both inside and outside of their service area to supply their utility customers as well as sell output to the market.