Is it a tax or is it not a tax? That’s the question in London, where diplomats are up in arms over a proposed daily fee on cars driving into the city center, in order to discourage congestion and clean up the city’s air. They say the fee most certainly is a tax, and that therefore embassies should be exempt from it under the 1961 Vienna Convention, which bars governments from levying taxes against such institutions. But Ken Livingstone, the famously contentious mayor of London, says it’s not a tax — a claim the U.S. is threatening to respond to by levying its own “non-tax” against British diplomats. Meanwhile, though, the diplomats are trying to solve the problem in the way they know best — diplomatically. George Kirya, the high commissioner of Uganda and the dean of the London diplomatic corps, is planning to approach the Livingstone government to plead the diplomats’ case, especially for poor countries, for whom the nearly $8 tax could be a financial burden.