The U.S. Supreme Court has lately polarized Americans with controversial verdicts on abortion, guns, climate change and more. Another case on its docket, by contrast, will get intense scrutiny mainly from millions of Americans living abroad.

Alexandru Bittner v. United States is about some of the tax and compliance rules the U.S. slaps on its own expats. These can be so draconian as to amount to criminalizing the sheer act of living outside the U.S.

Bittner is a businessman and a dual citizen of the U.S. and Romania. He used to live and work in Romania and, naturally, had to open financial accounts there. What he apparently didn’t know — many expats don’t — is that he had to declare all these accounts every year to the U.S. Treasury’s Financial Crimes Enforcement Network, on a form colloquially known as the FBAR.