Washington (CNN) The Supreme Court will meet behind closed doors on Friday to discuss whether to add cases to the court's docket next term, including one petition brought by a mystery company related to special counsel Robert Mueller's investigation.

If the court denies the case, it will represent the last stop for a company that has been fighting a subpoena issued last year by a federal grand jury in Washington, DC.

For months now, the case has been one of the most closely watched and guarded secrets among Mueller's work. The company, that calls itself a wholly owned agency of an unnamed foreign state, fought the subpoena arguing it was immune under a federal law called the Foreign Sovereign Immunities Act that limits such prosecutorial action.

It also said that complying with the request for documents would violate the country's own laws.

The case was so secret that at one point court security took the almost unprecedented step of clearing an entire floor of a courthouse in Washington to keep secret the identities of the lawyers arguing the case.

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