The president's commercial real estate company is coming under increasing scrutiny from special counsel Robert Mueller as he investigates potential Russian ties.

Mueller has subpoenaed The Trump Organization to turn over documents related to Russia and other topics he is investigating, the New York Times reports.

The subpoena represents the first known instance of Mueller requesting documents related to President Donald Trump's businesses and signals that the investigation could last for several more months.

Upon taking office, the president decided not to divest from The Trump Organization, which owns dozens of hotels, multifamily buildings, office towers and golf clubs around the world. Some of those properties have been reported to benefit heavily from Russian money, a trend that could be of interest to Mueller as he investigates Russia's interference in the 2016 elections.

At least 63 individuals with Russian passports or addresses have bought at least $98.4M of property in seven Trump-branded South Florida properties, a Reuters investigation found. The head of a political research firm testified to Congress in November that those sales to Russian nationals may have involved money laundering.

Mueller has already indicted 13 Russian nationals and four former Trump aides, including his former campaign manager, Paul Manafort, who has been charged with money laundering related to his real estate holdings and other financial crimes.