London Mayor Boris Johnson is raising a stink over minor congestion charges he says President Obama's motorcade incurred while visiting his city, the London Evening Standard reports.Johnson has fined the United States 120 pounds (nearly $200 U.S. dollars) in congestion levies--10 pounds per vehicle--for the presidential motorcade used during Obama's state visit in May. The sum may seem to be a pittance, but it is part of a much larger problem, Johnson and others say. London officials told AFP that the American Embassy owes 5.3 million pounds ($8.7 million dollars) in unpaid congestion fines--known as C-charges--which were first established in 2003. Since the roads weren't closed during the president's visit, he is subject to the fines, Johnson says. In speaking with the Standard, the Embassy defended its refusal to pay, citing the Vienna Convention on Diplomatic Relations, which prohibits "this sort of tax on diplomatic missions." The Standard reports that Obama's personal armored Cadillac--nicknamed "The Beast"--first escaped a fine because congestion charge cameras were unable to record its license plate number. As you may remember, "The Beast" encountered problems of its own on that UK trip. During a visit to the U.S. Embassy in Dublin, Ireland, Obama's car got stuck on the driveway in front of crowds of onlookers.