The master of a seagoing vessel flying the national flag of Estonia and engaged in domestic voyages or regular service from an Estonian port may only be an Estonian or EEA citizen, or a citizen of another state on the basis of reciprocity.
"§ 3.  Master of Estonian ship:
 (1) The master of a seagoing vessel flying the national flag of Estonia and engaged in domestic voyages or regular service from an Estonian port may only be an Estonian citizen or a citizen of a Contracting State [of the European Economic Area].

 (2) The master of a seagoing vessel flying the national flag of Estonia specified in subsection (1) of this section may also be a citizen of a state not specified in subsection (1) of this section if that state grants a similar right to the citizens of Estonia by an international agreement."
(Law of Ship Flag and Ship Registers Act (RT I 1998, 23, 321; last amended 25.11.2020), §3 [unofficial translation])
Law of Ship Flag and Ship Registers Act (RT I 1998, 23, 321; last amended 25.11.2020), §3 
[<a href="https://www.riigiteataja.ee/en/eli/ee/509122020003/consolide/current">Act</a>]