Monopolies may be either public (that is, government-operated) or private. Often, local telephone service is provided by a private monopoly. One favored private company is given a legal charter by the government, which enforces the monopoly by prohibiting all other sellers from providing competitive phone service. First-class mail service, on the other hand, is a public monopoly in the United States. Although other providers are technically permitted to deliver such mail, their customers are still legally required to pay postage to the government-owned monopoly. (In addition, private delivery services are prohibited from using the postal boxes assigned to their customers.) Similarly, the customers of private schools may still be required to subsidize state schools through taxes. In both of these instances, competition is technically permitted but severely restricted by coercive governmental policy. In other cases, competition may be prohibited outright. For instance, private companies are barred from coining money or issuing bank notes for gold deposits as they would in a free market (cf. pp. 4.6:31-5).