The Union of Eastern European Republics and the Eastern European Treaty Organization is formed by the Eastern European states Lithuania, Poland, Hungary, Romania, Slovakia and Yugoslavia-Albania. Greece gets observer status at the UEER. Both treaty are signed in 1964.6 București Treaty.
| Nation. | Year of joining. | Year of leaving. |
|---|---|---|
| Lithuania | 1964.6 | - |
| Poland | " | - |
| Hungary | " | - |
| Romania | " | - |
| Slovakia | " | - |
| Yugoslavia-Albania | " | - |
