Porsche is challenging London Mayor Ken Livingstone's plans to change the capital's Congestion Charge to an emissions-based system from October 27.
Livingstone announced last week that cars with carbon dioxide emissions above 225g/km would be charged £25 to enter the Congestion Charge zone. Sub-120g/km cars will enter the zone for free.
In a statement, Porsche said: 'The proposed increase is unfair, disproportionate and will do nothing for the stated aim of decreasing emissions in central London.'
Porsche has just two models, the entry-level Boxster and Cayman, that fall below the 225g/km cut-off.
It has written to Livingstone stating its concerns and has given him 14 days to respond. If he fails to do so, it says it will formally submit an application for a judicial review at the Royal Courts of Justice.
Kensington and Chelsea borough council has also been consulting lawyers, and may challenge the changes as well.
Legal experts claim a judicial review could be brought if it was possible to show that the Mayor had not followed proper procedure, had exceeded his powers, that the consultation process was insufficient or that the plans were irrational or disproportionate.
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