Chapter 13 debtors proposed a plan that paid secured creditors first, general unsecured claims second, and priority claims under 11 U.S.C. § 507 last, and the IRS objected. The court determined that 11 U.S.C. § 1322(a)(2) requires full payment of § 507 priority claims, but does not require payment of those claims in any particular order. However, relying on § 1322(b)(1), the court ruled that unsecured claims may be treated differently, under certain circumstances, so long as the different treatment does not result in unfair discrimination. Applying the four-part test in In re Wolff, 22 B.R. 510 (9th Cir. BAP 1982), the court concluded that debtor's failure to offer a reasonable basis for the discrimination prevented them from establishing Wolff's acceptable discrimination factors. The court then suggested that concurrent payment of the IRS and other unsecured creditors, on a pro rata basis, would likely not be discriminatory under § 1322(b)(1).