The RAC has raised concerns over the refusal by councils to install warning signs for the expanded Ultra Low Emission Zone (Ulez).
The expansion, effective from Tuesday, imposes a daily charge of £12.50 on some vehicles entering London.
Six out of the seven councils neighbouring the capital have not signed an agreement with Transport for London (TfL) to install warnings signs.
Many roads into London will therefore lack notice and drivers could be fined.
Kent has joined Hertfordshire, Buckinghamshire, Essex, and Thurrock councils in rejecting permission for signage.
Only Slough, the smallest neighbouring local authority, has reached an agreement with TfL.
The charge will apply if a vehicle fails to meet certain emission standards.
'Stop resisting'
Simon Williams, spokesperson for the RAC, said contesting or opposing the mayor of London's plan might not be the most effective approach.
He told BBC London: "I think the councils who are contesting or battling the mayor of London probably need to just give in and give drivers a little bit of advance warning."
He said it was important to provide drivers with effective communication through signage.
"I think people do need a good advance warning of the fact they're entering the Ulez zone so it's time that councils stopped resisting and actually go ahead and put up the signs so everyone approaching the zone from all directions has adequate warning," he said.
Councils bordering London have refused to install the advance-warning signs
Mayor of London Sadiq Khan has extended TfL's scrappage scheme to all London residents with non-compliant vehicles.
An additional £50m has been allocated to the initiative, which allows Londoners to trade in vehicles in exchange for grants of £2,000 for cars and £1,000 for motorbikes.
No support has been announced for people living just outside London who regularly commute into the city.
Martin Gough, the leader of Kent Council, said: "We're not prepared to facilitate a scheme against the interests of our residents and for which the mitigation others in London have been offered, have not been offered."
TfL has stated that London's deputy mayor for transport, Seb Dance, criticised the decision of the councils, asserting that they were "letting down residents".
Dance has argued that if drivers were fined due to a lack of warning about the Ulez, councils should bear the responsibility.
The mayor's spokesperson has previously said that the refusal to erect signage might make councils accountable for drivers not being "fully aware" of the Ulez boundaries.
They also highlighted that county highways authorities have statutory obligations and that the councils have declined TfL's offer to fund the sign installation costs.