Does a State violate subsection (b)(4) by exempting intangible-personal-property of non-railroads from its personal-property-tax, but not exempting such property for a limited group of taxpayers that includes railroads?

QUESTION PRESENTED The Railroad Revitalization and Regulatory Reform Act of 1976 (“4-R Act”), codified at 49 U.S.C. § 11501, limits state taxation of railroads in several ways. Subsections (b)(1)—(8) provide specific rules for state property taxes, requiring States to apply the same assessment ratio and tax rate to railroads that they apply to commercial and industrial property owners. 49 U.S.C. § 11501(b)(1)-(8). Subsection (b)(4) then prohibits States from “[i]mpos[ing] another tax that discriminates against [railroads].” 49 U.S.C. § 11501(b)(4). In Department of Revenue of Oregon v. ACF Industries, Inc., 510 U.S. 332, 347-48 (1994), the Court held that the 4-R Act “does not limit the States’ discretion to exempt nonrailroad property, but not railroad property, from ad valorem property taxes of general application.” The Court left open the question of whether a State would violate subsection (b)(4) if “railroads—either alone or as part of some isolated and targeted group—are the only commercial entities subject to an ad valorem property tax.” Id. at 346. The question presented is: Does a State violate subsection (b)(4) by exempting intangible personal property of non-railroads from its personal property tax, but not exempting such property for a limited group of taxpayers that includes railroads?