For the first time in my life, I was stopped for an immigration check, which was on a metro platform in Sofia (Bulgaria). A police officer told me something in Bulgarian, and when I said (in Bulgarian) that I don't speak Bulgarian, his face changed and he said "bla bla bla pasport!" whereby I showed him my ID. As he spoke no English, he silently gave it back after 45 seconds.
In which cities is this common for this to happen in the underground? I've heard of it being the case in Tashkent (Uzbekistan)