The ride-hailing company was taking a percentage out of the fare amount including tax, rather than a pre-tax amount, the New York Times reports. This means that if there was a $3 tax on a $20 ride, Uber would take its 25% share out of the $23 instead of the $20.

“We are committed to paying every driver every penny they are owed—plus interest—as quickly as possible,” Rachel Holt, Uber’s regional general manager for the U.S. and Canada, said in a statement to the Times.

But that may not be the end of the problem, as a drivers group says that Uber should not be taking the taxes out of the fares at all, but rather paying them out of its own take.

“Uber hasn’t just wrongly calculated its commission; it has been unlawfully taking the cost of sales tax and an injured-worker surcharge right out of driver pay,” the New York Taxi Workers Alliance said in a statement.

Uber is already facing fallout after announcing a new system that would not pass on increased rates to drivers. It is has also been dealing with a push from the New York City Taxi and Limousine Commission to require it to allow passengers to tip drivers within the app in New York City.