Branches of a credit institution established in a third country are subject to a license which is granted by the Bank of Greece on the basis of reciprocity.
"Article 36
Provision of services, with or without establishment, in third countries by credit institutions established in Greece 
Provision of services in Greece by credit institutions established in third countries (Article 47 (1) and (3) of Directive 2013/36 / EU)
[...]
2. For the establishment and operation in Greece of branches of a credit institution established in a third country, the license is granted by the Bank of Greece on the basis of the principle of reciprocity and without prejudice to the agreements concluded by the European Union pursuant to paragraph 3 of Article 47 of Directive 2013/36 / EU, provided that the following conditions are met:
a) before the start of operation of the first branch, there is a dowry capital, according to circumstance b) of par. 1 of article 12, which will be an equity position for the activity of the branch in Greece. The equity data of the branch are determined by a decision of the Bank of Greece,
b) the credit institution submits the data and information requested by the Bank of Greece, in order for it to form a clear picture of its activity in the exercise of its supervisory responsibility.[...]" (Law on the Access to the Activity of Banking Institutions 4261/2014), last amended by Law 4799/2021, Article 36 [google translation based on unofficial text at kodiko.gr])
Law on the Access to the Activity of Banking Institutions 4261/2014), last amended by Law 4799/2021, Article 36 
[<a href="http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wEc63YDhn5AeXdtvSoClrL8yNwbRNbiFj15MXD0LzQTLWPU9yLzB8V68knBzLCmTXKaO6fpVZ6Lx3UnKl3nP8NxdnJ5r9cmWyJWelDvWS_18kAEhATUkJb0x1LIdQ163nV9K--td6SIuYJV-2DjtTnPr9KeQkWebNTyV39LhYJMmiOnnbnQMVSc">Law (official)</a>],[<a href="https://www.kodiko.gr/nomothesia/document/79732">Law (unofficial)</a>]