Several embassies have suspended their congestion charge payments after the western extension came into force.
More than 60 foreign missions fall within the newly expanded zone encompassing Kensington and Chelsea.
They say the £8 charge is a tax from which they are exempt under the Vienna Convention on Diplomatic Relations.
London embassies owe millions of pounds in charges and fines for non-payment but they are protected from enforcement by diplomatic immunity.
The embassies of France, Germany, Belgium, Slovakia, Belarus, Russia all confirmed to the BBC News website they had suspended payments.
"Embassies that misuse diplomatic immunity to avoid the charge are enjoying the benefits of reduced congestion but contributing nothing"
Diplomats were settling congestion fee bills but now their offices are inside the charging zone, they have stopped paying.
A French diplomat said the embassy ceased payments on 19 February, when the western expansion went live.
"On Monday the situation changed for us because we are now in the congestion charge zone," the diplomat told BBC News.
"The charge is equivalent to a tax and it is contrary to the Vienna Convention."
A spokesman for the Russian embassy said: "Under the convention, all diplomats are free from local taxation."
In all, about 50 missions are refusing to pay the charge, according to the US embassy, which has clocked up more than £1m in unpaid fees.
However, Sweden, Israel, Netherlands, Iran, Syria and Finland were among several missions who said they would pay the charge.
The office of the mayor of London accused embassies of abusing their diplomatic privileges.
"Those embassies that flout the law of this country and misuse diplomatic immunity to avoid the charge are enjoying the benefits of reduced congestion but contributing nothing," said a spokesman.
"The UK government has made it clear to all embassies that the congestion charge is a charge, not a tax, and that diplomats should pay it.
"British diplomats pay such charges in other countries and we believe it is reasonable for us to expect diplomats to show equal respect for the laws of this country."
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