regulatory regime. Pan American, 366 U.S. at 663, 81 S.Ct. 1303("The rights asserted by Cities Services are traditional common-law claims. They do not lose their character because it is common knowledge that there exists a scheme of federal regulation of interstate transmission of natural gas."). Aild, in fact, the supplemental letter bore only an attenuated connection to the filed original contract. Id. at 660, 81 S.Ct. 1303. By contrast, the tariffs here directly implicate the federal regulatory regime, were filed with FERC, and concern obligations directly and exclusively arising under regulations issued pursuant to the FPA. California's state claim represented a naked attempt to enforce these federal obligations. Accordingly, we hold, as compelled by Sparta, L.Ed. 842 (1890) (<HOLDING>). Thus the Supreme Court has “understood the
holding that the eleventh amendment protects a state from suit by its own citizens holding state immune from suit involving a federal question holding state immune from suit brought by its own citizens holding state immune from suit brought in state court holding that sovereign immunity barred a federal question suit against a state brought by one of its own citizens even though the text of the eleventh amendment only addresses suits brought by citizens of another state