Black cab driver and GMB rep Ibrar Hussain says the number of hackney carriages in Sheffield has fallen from 857 to 631.
Drivers are given a licence for either a black cab or private hire but Mr Hussain is calling for more flexibility.
He said: “Black cab numbers are going down fast because drivers are moving over to private hire.
“Black cabs cost more than £58,000 and no one can afford them, especially under current financial circumstances as the pandemic has left the trade dead.
“Another issue is every customer now wants to pay via card but the majority of cabs don’t have that facility.
“The trade has been asking licensing services at Sheffield Council to review the hackney carriage policy.
“We want them to allow a mixed fleet of vehicles with saloon cars otherwise the black cab trade will be decimated.”
Coun Douglas Johnson, Executive member for transport, said the taxi trade had been hard hit by the pandemic.
“Even before Covid, drivers were giving up black cabs in favour of the changing market of Uber and, more locally, City Taxis.
“Many people find it easier to locate and pay for a cab via a smartphone app, which takes all the hassle out of handling cash for an individual fare. The demand for taxi ranks has fallen in comparison.
“Many cab drivers now offer card payment facilities which are available to small businesses and individuals at much more affordable costs.
“This has helped those drivers competing for trade, as people have used less cash over the pandemic.”
But he said black cabs provided a vital service for passengers in wheelchairs.
“A mixed fleet simply means that not all vehicles are accessible to disabled people in wheelchairs.
“This is a real concern, given that many disabled people are heavily reliant on taxis to get out and about.
“Disabled people tell of many cases where drivers still refuse to pick them up if they require assistance with a wheelchair.”