The US Supreme Court ruled in a split decision Tuesday that a provision in the 1855 Treaty between the Yakama Nation of Indians and the US preempts Washington state’s fuel tax.

The case before the court involved Cougar Den, a wholesale fuel importer incorporated under Yakama law. Cougar Den obtains fuel in Oregon and transports it using Washington state’s public highways, selling the product at gas stations located within the Yakama reservation. Because this transport of fuel involves public highways, the Washington State Department of Licensing argued that $3.6 million in state taxes, penalties and licensing fees were owed. The Yakamas, though, claimed that a treaty provision reserved a “right, in common with citizens of the United States, to travel upon all public highways.”

Writing an opinion joined by Justices Sonia Sotomayor and Elena Kagan, Justice Stephen Breyer noted that the treaty’s protection of the right to travel on public highways includes travel with goods meant for trade. A tax on certain goods would impose a burden on the protected travel and would not be consistent with a fair reading of the treaty. Furthermore, there is substantial precedent allowing the treaty to pre-empt state law in other circumstances, such as the purchase of fishing licenses, where conflict exists.

In a concurrence joined by Justice Ruth Bader Ginsburg, Justice Neil Gorsuch dismissed Washington state’s attempt to read the treaty “only as a promise to tribal members of the right to venture out of their reservation and use the public highways like everyone else.” Such a reading would betray the original understanding of the right-to-travel provision and would lead the Yakama to “be made prisoners on their reservation.” The Yakama’s ability to travel broadly and market freely is consistent with the treaty’s original intent.

The Court’s decision affirms the holding of a Washington Superior Court and the Washington Supreme Court that the state fuel tax was pre-empted.