Transport for London and Downing Street are facing an investigation from the Information Commissioner's Office, Liberal Democrat Caroline Pidgeon revealed in City Hall on Tuesday night (11 April).
The chair of the London Assembly's transport committee, speaking at a black cab event organised by Ukip's Peter Whittle and David Kurten, said she had asked the watchdog to launch the probe.
The development comes after emails and other documents, obtained by Pidgeon using the Freedom of Information Act, revealed that aides close to David Cameron urged Mayor of London Boris Johnson to drop proposed extra regulations on private hire app Uber in 2015.
Transport for London (TfL) dropped the plans, including making Uber customers wait five minutes between booking their car and starting their journey, in 2016 after more than 200,000 people signed a petition.
"That correspondence between Downing Street and TfL, those were my FoI requests. I have now got the Information Commissioner investigating because Number 10's response completely differed from TfL," Pidgeon said.
The comments come after hundreds of black cabs blocked Whitehall, Westminster, on 6 April over the revelations. Grant David, chairman of the London Cab Drivers Club (LCDC), urged Mayor of London Sadiq Khan to meet with his colleagues.
"The future can be rosy. but we need TfL to regulate [Uber and other private hire apps]," he added. "If they don't regulate, and we've got 120,000 mini-cabs doing the same job as me in a vehicle that's half the price and half the fair, we will just become a tourist attraction on the top of a tin of biscuits."
Helen Chapman, the general manger for TfL's taxi and private hire division, told the audience at City Hall that "we all want to work together to make sure that there's a great future and there's another 350 years of taxis in London, which are iconic and recognised around the world".
An Uber spokesperson said: "More than 200,000 Londoners signed a petition in autumn 2015 against plans for things like five minute minimum waiting times. They were also condemned by consumer groups, the media, and even the Competition and Markets Authority.
"While some of these absurd measures were dropped Transport for London is still pursuing proposals which would be bad for Londoners and drivers who use our app. For example, we are currently challenging through the courts plans for written English tests, which TfL's own estimates say would lead to 33,000 private hire drivers losing their livelihoods."
UPDATE: 11:40 BST, 12 April
A spokesperson for the ICO said: "Anyone who has asked for official information from a public authority and thinks they have wrongly withheld information or incorrectly handled a request can bring their complaint to the ICO. We are aware of the issues raised and are making enquiries."