In the period from circa November 1979 until 1984-04-30, the EZ prefix was used throughout the USSR by class 4 (beginner) stations. EZ licencees were restricted to 5w and could only operate on 160m. 


Thus EZ1A calls would be Leningrad, EZ0F  Sakhalin, EZ7L Kustanai/Kazakh SSR, EZ2R Estonian SSR, etc.


Information provided by Constantin M. Semyonov, UA1AKE.