This paperís purpose is to study the problem of a regulator of a utility monopoly, who has a universal service goal that is binding, in the sense that there is no twopart tari§ that can induce e¢ cient consumption, self-Önance the Örm, and guarantee universal access at the same time. The optimal two-part tari§s that the regulator should set under the following three di§erent regulatory rules are derived: no áexibility (the monopolist just o§ers the regulated plan), partial áexibility (the monopolist can o§er alternative plans, but these -and the regulated one- must be available to all customers), and full áexibility (the regulated plan must be available to all customers, but not the alternative ones). The solutions under the three schemes are characterized, and provide an unambiguous ranking of regulatory rules: total áexibility is weakly better than partial áexibility, with the latter being strictly better than no áexibility.