Federal prosecutors in Manhattan have opened an investigation into possible lending fraud in the New York City taxi industry, the most significant action taken so far in response to widespread practices that trapped thousands of cabdrivers under crushing debt, according to people with knowledge of the inquiry.

In the past month, agents have interviewed cabdrivers who said they were encouraged to take on massive debt under exploitative terms in order to buy a taxi medallion, the city permit that allowed them to own their own cab.

The investigation, which is in its beginning stages, appears to be looking at possible crimes including bank, wire or mail fraud.

The inquiry is being conducted by the United States Attorney’s Office for the Southern District of New York. It could reverberate throughout the city’s taxi industry, which has been engulfed in a financial crisis and rocked by a string of suicides among cabdrivers. More than 950 drivers have filed for bankruptcy, and many more are still buried in overwhelming debt today.