The Senate’s top tax-writers want to know why an Alabama appraiser named in a Department of Justice lawsuit involving some tax-advantaged land transactions known as syndicated easements surrendered his appraisal license in April.

The July 18 letter from Senate Finance Chairman Chuck Grassley (R-Iowa) and ranking member Ron Wyden (D-Ore.) to the executive director of the Alabama Real Estate Appraisers Board said that the DOJ alleged that Claud Clark III, the appraiser, took part in 58 such transactions “involving grossly overvalued appraisals.”

Clark surrendered his appraisal license in lieu of an administrative hearing into allegations of rule breaking, according to...