Sonoco Products Co. v. Michigan Department of Treasury

(1) Whether the Multistate Tax Compact has the status of a contract that binds its signatory states and requires them to allow taxpayers to elect to use the compact's equally weighted apportionment formula until the state prospectively withdraws from the compact; (2) whether Michigan's retroactive repeal of, and withdrawal from, the compact violated the contracts clause; (3) whether Michigan's retroactive repeal of, and withdrawal from, the compact violated the due process clause; and (4) whether Michigan's retroactive repeal of, and withdrawal from, the compact violated the commerce clause.