The increased charge will be introduced in October
London borough of Kensington and Chelsea has said it is an "interested party" in Porsche's legal bid to quash the proposed hike in congestion charge.
Porsche's legal challenge follows Mayor Ken Livingstone's plans to raise the daily levy on the most polluting cars from £8 to £25.
The council refused to elaborate but said it backs Porsche's case.
Transport for London (TfL) said it will "vigorously contest" the car giant's legal action.
Under the plans the highest carbon dioxide (CO2) emissions cars will be required to pay £25 congestion charge whereas cars with the lowest emissions will get a 100% discount on the charge.
The planned increase is due to come into effect on 27 October.
'Pointless legal action'
In February the £8 congestion charge zone was extended west to cover parts of Westminster and Kensington & Chelsea which TfL believe will cut congestion by 15%.
The council declined to give any details or comments before the 1 May elections for the City Hall.
Andy Goss, Managing Director of Porsche GB, said: "I am pleased that Kensington and Chelsea have joined us in our fight against this unfair, counter-productive tax against motorists.
"It is becoming increasingly clear that Londoners are rejecting this unfair £25 charge that will likely make congestion and global warming worse than it is today."
A TfL spokesperson said: "We will vigorously contest Porsche and Kensington and Chelsea's pointless legal action.
"It is important to encourage all Londoners, including residents of the Congestion Charge Zone, to switch to vehicles that emit lower levels of CO2.
Therefore residents with Band G or equivalent vehicles will not be entitled to the residents' discount."