The mayor said he will introduce more on-street inspections
London's mayor has been accused by opposition politicians of putting the safety of black cab passengers at risk.
Boris Johnson has announced plans to reduce taxi inspections from twice to once a year.
The new Conservative mayor said he would cut red tape and make the lives of cab drivers easier.
But the London Assembly Labour Group said it was a reckless move as more than a third of vehicles undergoing a mid-year inspection failed the test.
It said Transport for London (TfL) figures showed nearly 10% of those failing the test failed because of problems with brakes or shock absorbers.
The Licensed Taxi Drivers' Association (LTDA) said most failures were due to paperwork.
The mid-year inspections were introduced in October 2007 by then Labour mayor Ken Livingstone and were accompanied by a £36 increase in the annual licence fee, from £142 to £178, to cover the cost of the additional test.
Mr Johnson has launched a consultation over whether to scrap the twice-year inspection and reduce the annual licence fee.
He also said he would increase the number of on-street taxi inspections by TfL's vehicle compliance team.
The on-street inspections are not as thorough as the mid-year inspections, the LTDA said.
But Val Shawcross, from the London Assembly Labour Group, said: "The thing that people forget about cabs is that they are on the road all the time.
"Sometimes they are shared between a couple of drivers and they do clock up a lots of miles in very difficult driving conditions.
"And the fact that so many do need to get something fixed does speak volumes for the need to keep up these checks."
Mr Johnson said: "Mid-year taxi inspections have proved an unnecessary burden for drivers and owners, and have penalised the majority who maintain their vehicles throughout the year.
"This consultation proposes a fairer system, where the industry benefits from a simpler and cheaper inspection regime.
"Only those few taxi drivers whose vehicles do not meet required standards will have to pay for follow-up inspections."
Bob Oddy, general secretary of the LTDA, said: "The mid-year inspection was brought in by the previous administration - so it is no surprise the Labour group has objected."
A Public Carriage Office spokesperson said it would consult the taxi trade on a new inspection regime.
He said: "Should we decide to go ahead with the proposal to increase on-street inspections, we will be reviewing what changes or enhancements might be required to maintain and improve standards within the taxi industry."