Washington (CNN) One law firm involved in a foreign government-owned company's challenge of a mysterious grand jury subpoena related to the Robert Mueller investigation is Alston & Bird, CNN has learned, a firm that has previously represented Russian interests, including working for a Russian oligarch and a contractor of the Russian government.

CNN's reporting of the law firm's identity is among the first details revealed about a case that's progressed to the Supreme Court under extreme secrecy.

The identity of the foreign government and the company has been a closely held secret, and after several setbacks in court, the company may be forced to give the special counsel's office information or face a steep financial penalty.

Attorneys involved in the case include DC-based white-collar lawyer Ted Kang and Brian Boone, a North Carolina-based appellate attorney. It is not clear whether they represent the company, the country's regulators or another interested party.

Kang says on his professional website he represents "numerous entities and individuals in connection with" Mueller's investigation.

He is also experienced in international work, listing among his past clients Korean and Australian companies. And Boone lists among his past clients the Republican National Committee regarding public records litigation.

Kang, Boone and firm leadership have not responded to multiple inquiries from CNN over the past several months. The firm's involvement in the case gives a few clues to whom its client may be.

Typically, large law firms like Alston & Bird represent masses of clients among their hundreds of partners. Only when a client allows it may a firm publicly acknowledge whom they represent. The Washington Post reported Tuesday night that the company is a foreign financial institution, citing two sources familiar with the case.

Lawyers in closed-door hearings

CNN first spotted the mystery court activity in September last year, when lawyers appeared in the courtroom for DC District Court Chief Judge Beryl Howell opposite five prosecutors from Mueller's team. At that time, one of the corporate lawyers told CNN he was from Alston & Bird and represented "a country."

Another mystery court hearing before Howell happened in October, with Kang and Boone opposite Mueller's team, including top criminal appellate advocate Michael Dreeben.

After the hearing, a CNN reporter approached Kang and Boone about their client but they declined to comment.

After Howell denied the company's challenge twice, the case then moved to the US Court of Appeals for the District of Columbia Circuit. Politico reported at that time that the appeals case related to Mueller's investigation.

When the scheduled arguments happened in December before the three-judge appellate panel, court officials were so careful not to reveal the identities of the lawyers involved that they cleared the public and media from an entire floor of the DC federal courthouse.

The company lost its challenge of the subpoena soon after. At that point, the DC Circuit judges were able to say that the subpoena sought information from a foreign state-owned company. They revealed little else about the case.

The company then took its fight to the US Supreme Court. On Tuesday, the Supreme Court denied it would continue to freeze daily fines placed upon the company for noncompliance. The court also said the company could file its broader challenge of the subpoena and its legal reasoning with some details still confidential. If and when that filing comes in, it could identify the appellate lawyers involved on both sides.

JUST WATCHED The man who oversees Mueller's investigation Replay More Videos ... MUST WATCH The man who oversees Mueller's investigation 01:02

Alston & Bird

Alston & Bird's history of working for Russians dates back to the early 2000s.

The Russian oligarch Oleg Deripaska, a business contact of former Trump campaign chairman Paul Manafort whom Mueller's team has sought information about, paid Alston & Bird $300,000 upfront in 2003 to help him reinstate his US visa, according to public lobbying disclosure filings. Over the next few years, Deripaska paid the firm another $270,000 for their work, the filings say. Around that time, Deripaska gave Manafort a $10 million loan, which the FBI cited in a 2017 search warrant on Manafort.

The law firm is one of the largest in the world by revenue and one of the US' 50 largest law firms, according to legal industry data. The firm operates only two international offices, in Beijing and Brussels.

In a tense situation like the Mueller investigation, it's likely the firm's representation of the company and foreign state fall in line with past clients, so as not to pose ethical or business conflicts.

Alston & Bird's most well-known employee is former Senate Majority Leader Bob Dole, who has contributed to the firm's foreign and domestic lobbying business for years. The lobbying side of the firm works directly for two foreign governments, Kosovo and Taiwan, according to foreign lobbying disclosures.

The firm has also had a lobbying team focus on reform of the Foreign Sovereign Immunities Act -- the same law at issue in the mystery company's grand jury challenge.

It has also done work for global public relations firm Ketchum Inc., which hired it to "provide advisory services to Ketchum, Inc. for the Russian Federation." This included gathering information on contemporary US-Russia relations and monitoring "legislative developments in the Congress in similar issue areas," according to filings from 2014.

For years, Ketchum helped the Kremlin and state entities like Gazprom with public relations campaigns intended to influence US public opinion and policy.