The High Court has granted a number of councils permission to challenge plans to expand London's ultra low emission zone (ULEZ).
Five councils, including Bexley and Bromley, launched legal action in February over Sadiq Khan's plans to extend the zone from August 29.
If plans go ahead, drivers of vehicles which do not meet the emissions standards will have to fork out a £12.50 daily fee to drive in outer London, including those crossing into the border from Kent.
The plan to expand ULEZ has caused a stir among residents on both sides of the London-Kent border, with protestors last month taking to the streets of Orpington.
Tractors spiralling on roundabouts joined the protest, with some saying agricultural workers who are already struggling will be hit hardest by the charges.
The Mayor of London, however, has described the impact of ULEZ so far as “transformational” and claimed extending it will mean “five million more people will be able to breathe cleaner air and live healthier lives”.
The mayor insisted that the rising cost of living was a “key consideration” in his decision on whether to implement the proposal, and said it "has not been an easy decision".
High Court judge Sir Ross Cranston has now ruled that a judicial review can go ahead, with a one-day hearing set to be heard in early July.
Councils involved in the legal challenge argue the move to expand ULEZ did not comply with "relevant statutory requirements", and that expected compliance rates in outer London were not considered.
The councils also believe the proposed scrappage scheme, which would see eligible Londoners be granted financial assistance to scrap their high polluting vehicles, was not consulted on, and that the overall consultation process was not properly conducted, with a failure to carry out cost-benefit analysis.
The High Court has allowed the case to proceed, but only on the legal basis for the scheme, and scrappage.
A spokesman for Mr Khan said: "The mayor is pleased to see the court has refused permission for the majority of the grounds.
“We will continue to robustly defend this life-saving decision to expand the ULEZ and continue with preparations without delay.
“It is a shame that some local authorities have chosen to attempt this costly and misguided legal challenge instead of focusing on the health of those they represent.
“Around 4,000 Londoners die prematurely every year due to air pollution.
“This is a health emergency and the mayor is not prepared to stand by and do nothing while Londoners are growing up with stunted lungs and are more at risk of heart disease, cancer and dementia due to our toxic air.”
Leader of Bexley Council, Baroness O'Neill, said yesterday the ULEZ expansion proposal was "never about air quality".
She added: "We believe it would have disastrous consequences for many of our residents and businesses, as well as others who regularly travel into the borough.
“We hope that today’s decision moves us a step closer to stopping the Mayor’s money-making scheme.”
Bromley Council leader Colin Smith said there was "still time for the Mayor to pull back and take a more considered approach".
He continued this would benefit those "threatened by the horrendous daily cost of his proposed tax".
Baroness O’Neill of Bexley, leader of Bexley Council, said on Wednesday that the ULEZ expansion proposal was “never about air quality and we believe it would have disastrous consequences for many of our residents and businesses, as well as others who regularly travel into the borough”.
“We hope that today’s decision moves us a step closer to stopping the Mayor’s money-making scheme,” she added.
Bromley Council leader, Colin Smith, said there was “still time for the Mayor to pull back and take a more considered approach” to benefit those “threatened by the horrendous daily cost of his proposed tax”.
In February a petition was made for Bexley and Bromley to rejoin Kent due to the upcoming extension, as both boroughs were until 1965.
Dartford residents have said they feel "exiled" by the expansion, with people living on the border between Kent and London facing the daily charge for day-to-day tasks such as work, leisure, hospital appointments, or visiting friends and relatives.
Dartford Council leader Jeremy Kite in January described the plan as "a terribly, terribly, unfair thing".
He continued: "They might say it only affects a small proportion of drivers but they are the ones least able to afford it."