That's not something you see every day: an opinion from the U.S. Supreme Court that makes a reference to cryptocurrencies.

On June 21, the Supreme Court issued a ruling on Wisconsin Central Ltd. v. United States, a court case involving a dispute over whether worker stock options can be taxed as a kind of "compensation" in the same way that money is.

According to Ballotpedia, subsidiaries of the Canadian National Railway Company lost their initial court battles, with both a district court and, later, an appellate court, ruling that the stock options are taxable under the U.S. Tax Act.

However, the ruling made Wednesday by the Supreme Court has confirmed stocks do not count as "money remuneration" and the case should be "remanded for further proceedings consistent with this opinion," according to majority opinion issued Thursday.

The dissenting opinion, drafted by the 79-year-old associated justice Stephen Breyer and backed by Justices Ginsburg, Sotomayor and Kagan, argues that the nature of what constitutes "money" is less rigid than the majority's interpretation, noting that "what we view as money has changed over time."

That's a notable argument coming from the more conservatively minded Supreme Court, setting the stage for what is the first reference to bitcoin in a U.S. Supreme Court ruling.

Breyer wrote:

Such a statement raises a key question, given the source: what are the implications of this?

While the opinion, in this case, has nothing to do with cryptocurrencies directly, the passing reference nonetheless signals that at least some of those that make up the top U.S. court are sympathetic to the idea that a cryptocurrency is a kind of money, as opposed to a form of property (as the Internal Revenue Service has ruled) or commodity (in the view of the Commodity Futures Trading Commission and, more recently, a U.S. district court judge).

Perhaps it's far too early to say – but it's not impossible that questions about the nature of bitcoin could one day make their way to the Supreme Court.

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