The Taxi and Limousine Commission has discovered that some city cab drivers bilked passengers out of more than $8 million over the last two years.
The TLC said some cab drivers were switching the rate code for trips within the city to a higher code that is only supposed to be used for trips outside the five boroughs.
When the higher code is used, the rate doubles from 40 cents per one-fifth of a mile to 80 cents.
The TLC made the discovery using Global Positioning System technology and said the scam was primarily done by a small number of drivers who did it repeatedly.
City officials said more than 35,000 drivers illegally charged a rider at least once and 3,000 drivers were found to have doubled the meter rate more than 100 times.
The mayor said on Friday that the drivers could face serious charges.
However, the New York Taxi Workers Alliance blamed the same GPS technology, calling it a "systematic failure" with no actual witnesses to the allegations.
"It is so bad for the driver. It is more stressful and it is more ticketing for the driver and sometimes it's the technology that fails and it's not the drivers fault," said Javaid Tariq, the co-founder of the Taxi Workers Alliance.
The difference amounted to between $4 to $5 more per trip.