New York City has presented President Donald Trump's longtime personal attorney, Michael Cohen, with an ultimatum: divest from your taxi cab medallions quickly, or have them all seized.

In a letter to Cohen obtained by CNBC, a lawyer for the city's Taxi and Limousine Commission told Cohen that the agency plans to take his medallions in light of the five counts of felony tax evasion he pleaded guilty to earlier this week.

The TLC's prosecuting attorney, Andrew Rabin, wrote that the commission "intends to revoke all medallions" from Cohen unless he divests and transfers them to someone approved by the city.

Cohen now has until Sept. 10 to complete the transfer of 10 taxi cab medallions. But it might not be so easy to find willing parties to take them.

New York's ubiquitous yellow cabs require pricey, city-approved medallions, or licenses, in order to legally operate in the city.

Recent news articles say that there are fewer than 14,000 such licenses in the city, and that their value has been dropping precipitously as ride-hailing services such as Uber and Lyft take hold in metropolitan areas around the country.

Medallions once sold for well over $1 million apiece; they're now mostly worth a fraction of that price.

Even if he can't find willing customers for his medallions Cohen likely has bigger problems to worry about at the moment.

On Tuesday, he pleaded guilty to eight charges lodged by Manhattan federal prosecutors, including tax fraud and campaign finance violations.

Cohen was being watched by federal authorities for months before the investigation exploded into public view in April, when his hotel room and office were raided by FBI agents, who seized thousands of documents, along with recordings and electronic devices.

As part of the deal he struck with prosecutors, Cohen now faces up to 63 months in prison.

A spokeswoman for Cohen declined to comment on the letter.