Allegheny Pittsburgh Coal Co. v. County Commission of Webster County
In Allegheny Pittsburgh Coal Co. v. County Commission of Webster County, 488 U.S. 336, 109 S.Ct. 633, 102 L.Ed.2d 688 (1989), the Supreme Court concluded the defendant county denied the plaintiffs equal protection by setting their property tax assessment at 50% of market value based on recent purchase sale prices, but taxing other property owners at 50% of market value based on old appraisal values of their land (that had not been recently sold). Id. at 338-42, 109 S.Ct. at 635-37.
"This practice resulted in gross disparities in the assessed value of generally comparable property," thereby denying the plaintiffs equal protection. Id. at 338, 109 S.Ct. at 635.