Hanoi's transport department is seeking permission from the central government to limit the number of Uber and GrabTaxi cars to prevent severe traffic jams in the downtown area.
The department said that the ride-hailing services have added thousands of cars to compete with traditional taxi companies.
Since 2011, the city has stopped licensing new taxi firms and also stopped existing ones from expanding, keeping the total fleet at nearly 18,700 cars, it said.
The new services had around 2,364 cars as of the middle of November, it said.
Uber came to Vietnam in 2014 and GrabTaxi in June last year.
The services are still trying to find some legal support in Vietnam, with industry insiders saying local taxi firms are campaigning against it.
Prime Minister Nguyen Tan Dung has approved a transport ministry proposal requiring Uber to sign contracts with licensed transport companies instead of partnering with independent drivers like in other countries.
GrabTaxi cooperated with several taxi firms in Vietnam at the beginning but has added its own cars recently.
Ho Chi Minh City this year have fined 106 Uber and GrabTaxi cars for offering unlicensed transport services and creating unhealthy competition with other taxi firms in the city.