The Federal Bureau of Investigation is probing to see if Uber Technologies had used software to illegally interfere with its competitors, the Wall Street Journal reported on Friday.
The investigation is focusing on Uber's program that could track drivers working for rival service Lyft, the WSJ said, citing people familiar with the investigation.
The investigation is being led by the FBI's New York office and the Manhattan US attorney's office, the Journal said.
Separately, Uber will cease using diesel cars in London by the end of 2019 and the vast majority of rides will be in electric or hybrid vehicles by then, the taxi app said on Friday.
At the moment the company says around half of all the journey miles completed in the British capital are undertaken with greener vehicles on the firm's standard low-cost UberX service, which lets customers book journeys on their smartphone.
Several carmakers have announced plans in recent months to electrify a large proportion of their new cars, with Volvo becoming the first major carmaker to set a date for phasing out vehicles powered solely by the internal combustion engine.
Britain will ban the sale of new petrol and diesel cars from 2040, replicating plans by France and cities such as Madrid, Mexico City and Athens.
Uber, which has about 40,000 London drivers, will only offer electric or hybrid models on UberX by the turn of the decade and plans to do the same by 2022 nationwide.