Washington (CNN) FBI agents who raided the office of President Donald Trump's personal attorney Michael Cohen sought information about taxi owners who had financial dealings with Cohen, according to sources familiar with the search warrant.

The warrant, in addition to seeking other records and documents, specifically identified Semyon and Yasya Shtayner, Ukrainian immigrants who own a large taxi operation in Chicago, according to the source. Cohen is listed as someone who repeatedly loaned money to the Shtayners within the past 10 years, according to public records reviewed by CNN.

The interest in Cohen's communications with the Shtayners indicates US prosecutors are digging deeper into Cohen's personal financial dealings, including his taxi medallion business. The warrant, as CNN previously reported , is also seeking records and communications related to efforts to suppress negative information ahead of the presidential election, including communications Trump had with Cohen regarding the infamous "Access Hollywood" tape that captured Trump making lewd remarks about women and surfaced a month before the election.

The FBI's intensifying interest in Cohen could put new pressure on one of Trump's closest confidants as special counsel Robert Mueller continues his investigation into what the Trump team knew about Russian attempts to influence the 2016 election.

Cohen's attorneys were in court Friday seeking a temporary restraining order in New York to halt investigators' review of the seized evidence.

The Shtayners' connection to Cohen

The Shtayners emigrated to New York City from Ukraine at least four decades ago. Semyon Shtayner started out driving taxis, according to a 1979 article in The New York Times , and by 2004 was involved in the taxi business in Chicago setting up limited liability companies in his wife's name as well as those of others, according to CNN research of public records.

The Shtayners run one of the largest taxi operations in Chicago and own more than three dozen medallions. Taxi medallions, which were once very valuable, are licenses that give the owner a right to operate taxicabs in a particular city. Values have plummeted with the arrival of ride sharing operators Uber and Lyft.

Cohen is listed as a "secured party" for 22 of the shell companies associated with the Shtayners, indicating he loaned them money over the past decade, according to an expert familiar with taxi financing, who asked not to be named because his client had not authorized him to speak publicly. It isn't clear what Cohen received as collateral, but the expert says it has likely lost value since medallion values have fallen so sharply.

When medallions were increasing in value, it was common for owners to refinance to take cash profits from the business. But the drop in value has squeezed many operators, forcing some to sell medallions in foreclosure sales.

New York City medallions were valued in 2014 at an average of $1 million per medallion, according to the New York Attorney General's office. Last month, medallions sold in foreclosure for as little as $175,000 and an average of $355,131, according to city records.

The Shtayners fell behind on monthly payments on their loans to Signature Financial, and in 2016 the bank sued them. A private settlement was reached.

The couple has not been accused of any wrongdoing. It is not clear what prompted the FBI's interest in Cohen's communications with them.

The Shtayners did not return calls seeking comment. A lawyer who represented them in the 2016 lawsuit also could not be reached.

How Cohen got into the taxi business

Cohen's foray into the taxi medallion business preceded his time as Trump's personal attorney, but it continued to be a business he managed after he started working for Trump.

Cohen began buying taxi medallions in New York in earnest in the 1990s. He told The Washington Post that he bought some medallions from his wife's parents, who were also in the taxi business. Her father, Fima Shusterman, who also emigrated from the Ukraine, pleaded guilty in 1993 to a financial crime relating to the taxi business, according to court records.

By 2009, Cohen shifted his focus for the taxi business to Chicago. He continued to buy medallions until 2014, when his last purchase was recorded, according to the CNN review.

That same year, Cohen and his wife, Laura Cohen, took out several loans of unspecified value from Sterling National Bank, according to public filings. They put up the medallions as collateral.

A message left with Sterling National Bank was not immediately returned.

Laura Cohen was not named in the search warrant, according to one source.

The FBI search warrant also sought information about Cohen's communications with Sterling National Bank, The Washington Post reported.

Cohen took out one loan from Sterling National Bank in December 2014 for an unspecified amount using three of taxi companies as collateral, according to public records and the Post . Cohen also obtained a $1.98 million loan with his in-laws from the bank in 2015, the Post said, citing public records. It is not clear how the Cohens used the proceeds of the financings.

None of Cohen's taxi businesses have been accused of any wrongdoing. But his companies are not without their financial problems.

Cohen's taxi companies owe New York state $85,752 in taxes, according to state warrants filed on six of Cohen's shell companies since 2017, according to CNN research.

Correction: This story has been updated to correct the spelling of Shtayner.