Unlike Uber, Lyft deducts the additional 11.4 percent from what drivers receive even when there is no sales tax — as when a ride begins in New York and ends in Connecticut. This would appear to be a more egregious deduction, since it amounts to a transfer from the driver to Lyft’s bottom line, with no tax rationale to support it. But Lyft denies that the 11.4 percent charge funds tax payments specifically, as opposed to offsetting a number of costs.

Finally, like Uber, Lyft has accounted for sales tax differently in other states than it does in New York. In some other states that levy a tax, Lyft has assessed the tax on top of the fare the driver receives, making clear that the passenger pays it, and raising questions about the accounting in New York.

What are city and state authorities doing?

Allan Fromberg, an official with the New York City Taxi and Limousine Commission, wrote in an email that the agency had been examining the way Uber deducts the state-mandated sales tax and workers’ compensation surcharge from fares, as well as the way the company took its commission. Mr. Fromberg said the inquiry had been going on for weeks before Uber’s acknowledgment in late May that it had erred in how it took its commission.

A representative of the New York State Department of Labor, when asked in May whether the department had looked into improper sales tax deductions or planned to do so, responded that the department “has not received any complaints on this issue.”

Assemblyman Robert Rodriguez, who represents East Harlem, has written to the state attorney general and the state Department of Taxation and Finance calling for an investigation into Lyft’s practice of deducting 11.4 percent from driver earnings on rides that begin in New York and end out of state.

When asked about the possibility that Uber and Lyft had improperly deducted sales tax on in-state rides, he said that, if true, “that’s a much higher level of magnitude.” He said that state and city regulators should look into the handling of taxes and that “if it hasn’t been done correctly, they” — Uber and Lyft — “should fix it and make amends.”

Kimberley McGee contributed reporting.