Construction magnate Tony Accurso has lost his attempt to dodge having to testify at the Charbonneau Commission.
He had been fighting a subpoena since last summer.
When the Quebec Court of Appeal refused to hear his case, he went to the Supreme Court.
The high court announced this morning that it would not hear Accurso's arguments.
Accurso's name has come up frequently at the corruption inquiry.
The entrepreneur claimed that that being compelled to testify would put him in a possibly compromising position.