Internal passports were a standard Soviet thing and even continued in the independent Russia for a while (I assume got abolished by now, but maybe not).

Okay, I assumed wrong. The Pedia:

After the breakup of the Soviet Union in 1991, the Soviet Union internal passport continued to be issued until 1997, when a new regulating decree was adopted by the government and when it was replaced by the Russian internal passport.[1] The current Russian internal passports were first issued in 2007.[2]

Internal passports were a standard Soviet thing and even continued in the independent Russia for a while (I assume got abolished by now, but maybe not)