Once upon a time secured tax claims furnished a wonderful way to satisfy the One-Impaired-Class-Must-Accept-The-Plan Rule (by stretching out their payment or paying them less interest than they might otherwise be entitled).
But this tactical maneuver is no longer available because the BAPCA amendments require that a Chapter 11 plan provide for payment of a secured tax claim under the same rules that govern unsecured priority tax claims. Accordingly, a secured tax claim cannot be impaired and must be paid no later than five years after the bankruptcy filing and on terms no less favorable than the most favored nonpriority unsecured claim provided for by the plan (with the exception of the treatment to the administrative convenience class under Section 1122(b)).
Bankruptcy Code ยง 1129(a)(9)(C), (D). See also BAPCA, Confirmation Requirements, One-Impaired-Class-Must-Accept-The-Plan Rule.