Is a payment made under duress recoverable under a theory of unjust enrichment?

One may not recover under a theory of unjust enrichment a payment made to a unit of government unless it was made under coercion (Brumagim v. Tillinghast (1861) 18 Cal. 265). A person who, at the time of payment misinterprets the law to his detriment does not thereby gain a right of recovery; he must have paid as a result of compulsion. (Id., at pp. 270--271.)

Thus, in Garibaldi v. City of Daly City (1943) 61 Cal.App.2d 514, 143 P.2d 397, plaintiffs challenged a special assessment levied by the city. Plaintiffs paid the assessment under a threat that bonds would be issued against the property. Holding that the plaintiff had no right to recovery, the court said that even if the city employed duress, a protest by plaintiff was required. 'While it is true that in California certain cases have held that payments made under duress or compulsion without a formal protest are recoverable, such cases are distinguishable from the one before us. All those which independent research has disclosed involve sets of facts in which a formal protest would have been unavailing and in which the collector was aware of the claimed invalidity of the tax collected. . . . A protest serves not only to warn the recipient that he must be prepared to refund the money and must guide his acts accordingly, but also to make the recipient aware of the nature of the claimed illegality. Where, as in the cited cases, the collector is aware of the claimed illegality, either by other protests of similarly situated individuals or the forceful nature of the collection method, the collector can protect himself.' (Id., at pp. 516--517, 143 P.2d at p. 398.)