In 1991 when Estonia held a referendum to gain independence from the Soviet Union.
The first challenge of the independence process was what to do with the 500,000 mostly Russian.
TheSupreme Council decided on November 11, 1991 to require the naturalisation of all Soviet-era immigrants to Estonia while automatically renewing the citizenship of all prewar citizens and their descendants.
The Congress of Estonia decided that those immigrants and their children were not automatically citizens.
They would have to be "naturalized" by meeting language and residency criteria.
They were born in Estonia, they do not have Estonian citizenship, they have a grey passport, they are "Alien".