What kind of controversy gets the Supreme Court to line up Alito, Roberts, Kennedy, Breyer, and Sotomayor against Ginsburg, Scalia, Kagan, and Thomas? A suit over whether Maryland counties (and the city of Baltimore) must give credits to Maryland residents who pay taxes to other states for income they earn across state lines. This looks like a classic quarrel over whether the problem with a law is that it's lousy policy or that it violates the Constitution. What Constitutional principle limits taxes, you may wonder, and where has it been all our lives? In this case, the idea is that double-taxation across state lines amounts to a tariff on interstate commerce. If you don't find that convincing, you may side with strict-interpretationists Scalia and Thomas, and wish that the problem would be solved at the ballot box instead.
The press is generally reporting this as problematic because Maryland counties and the city of Baltimore need lots of cash, which apparently is the only useful consideration when it comes to taxation policy or the Constitutional limits on state power. Myself, I'd worry more about having to mediate disputes between states over who has the best right to glom onto every penny of income they can identify in the hands of people who are energetic enough to earn money in interstate commerce--but I suppose they've been facing that issue for a long time now, given that most states already have a system of interstate credits in place. Ah, for the days when I paid income tax to California, New Jersey, and the State and City of New York while living in (income-tax-free) Texas. I'm sure they put the money to good use.