The states who filed the brief in support of Montana are New York, Arkansas, California, Connecticut, Delaware, Hawaii, Idaho, Illinois, Iowa, Kentucky, Maryland, Massachusetts, Minnesota, Mississippi, Nevada, New Mexico, North Carolina, Rhode Island, Utah, Vermont, Washington, West Virginia and the District of Columbia.
Good on those states!

(Including mine, good to see.)
This is some pretty substantial pressure on the SCOTUS. It should be interesting to see what it decides about this.