Non-EU nationals may not acquire more than 49 per cent of shares in a shipping company. Non-EU  ownership of Greek flag vessels is limited to 49 per cent. Cabotage is reserved to national and EU flag vessels. 
"Article 10 - Restrictions on the acquisition of shares
1 . Nationals or legal entities of countries which are not members of the European Union or which do not belong to the European Economic Area are prohibited from acquiring rights in rem to shares in a shipping company.
2 . Exceptionally, it may be stipulated in the corporate agreement that the natural or legal persons referred to in paragraph 1 may acquire shares representing less than fifty per cent of the respective share capital. [...]" (Law on the Shipping Company (959/1979), last amended by Law 2987 / 2002, Article 10  [google translation based on unofficial text at kodiko.gr])
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"Article 5 - Terms of identification of ships as Greek
1. Ships belonging to more than fifty percent to Greek nationals or to Greek legal entities or to nationals of other Member States of the European Union or to Companies of other European Union countries referred to in Article [48 of the Treaty establishing the European Community] shall be recognized as Greek, at the request of their shipowners, accompanied by the relevant title deed.
2. In the case of companies of the other Member States of the European Union for the recognition of the merchant ship as Greek it is necessary to establish them within the meaning of Article 43 of the Treaty of the European Community, while for the natural persons of the other Member States of the European Union The installation requirement must be met by the time the ship is registered. In this context, the management of the ship is required to be exercised by Greece. The representative or guarantor appointed during the registration of the ship, as well as the natural person or the representative of the legal entity, who exercises the management, will be established in Greece.
3. The provisions hereof shall apply mutatis mutandis to nationals or companies of the Member States which are Contracting Parties to the Agreement on the European Economic Area (EEA).[...]" (Public Maritime Code (187/1973), last amended by Law 4770/2021, Article 5 [google translation based on unofficial text at kodiko.gr])
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"Article one - Maritime transport to or from island ports
1, From 1 November 2002, the provision of maritime transport services which: a) are provided for remuneration by a shipowner of a Member State of the European Community (EC) or of the European Economic Area or the European Free Trade Association (EC, G, EC), except Switzerland, and (b) are carried out between mainland and island ports or between island ports, by regular passenger and ferry line, as well as from ships with a total tonnage of up to six hundred and fifty units of calculation, in accordance with the international convention "On the measurement of the tonnage of ships of 1969", ratified by Law 1373/1983 (Government Gazette 92 A), if these ships are registered in Greece or another Member State of the EC. or of E, O.X.
2. Shipowner in this law means the person defined in the provision of paragraph 2 of article 2 of the Regulation (EOK) with Council No. 3577/1992 "for the application of the principle of free movement of maritime transport services within the Member States (maritime cabotage) "- L364 / 7-10 / 12-12-92,
3 . Exceptionally, if the ships provided for in paragraph 1 are insufficient, the provision of the sea transport services by ships carrying the flag of another state, subject to reciprocity and subject to the conditions laid down in that law.[...]" (Law on Maritime Cabotage (2932/2001), last amended by Law 4676/2020, Article 1 [google translation based on unofficial text at kodiko.gr])
Law on the Shipping Company (959/1979), last amended by Law 2987 / 2002, Article 10 
Public Maritime Code (187/1973), last amended by Law 4770/2021, Article 5
Law on Maritime Cabotage (2932/2001), last amended by Law 4676/2020, Article 1
[<a href="http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wGrY_r85_PxvndtvSoClrL8V8YeS8scMDB5MXD0LzQTLWPU9yLzB8V68knBzLCmTXKaO6fpVZ6Lx9hLslJUqeiQPWSTfgyHTH_ucT1l5TAj7-cbGxnqn4cTKIXMMY0D_6w.">Law (official)</a>],[<a href="https://www.kodiko.gr/nomothesia/document/305831">Law (unofficial)</a>],[<a href="http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wF6rlIz2Gsd0ndtvSoClrL8_q7ut2PVjhp5MXD0LzQTLWPU9yLzB8V68knBzLCmTXKaO6fpVZ6Lx3UnKl3nP8NxdnJ5r9cmWyJWelDvWS_18kAEhATUkJb0x1LIdQ163nV9K--td6SIuXwNRaSdoxMmeoicJgJs0hbHzGWvR-qmVSvb-xL4JzBN">Code (official)</a>],[<a href="https://www.kodiko.gr/nomothesia/document/500342">Code (unofficial)</a>],[<a href="http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wHgzIpqlooT4HdtvSoClrL8-zFLpBf_Zex5MXD0LzQTLWPU9yLzB8V68knBzLCmTXKaO6fpVZ6Lx3UnKl3nP8NxdnJ5r9cmWyJWelDvWS_18kAEhATUkJb0x1LIdQ163nV9K--td6SIuQYGsVqrCY0Tz_hXD1YCGJeyGeIoFdQLrPavfEv6heP6">Law (official)</a>],[<a href="https://www.kodiko.gr/nomothesia/document/184769">Law (unofficial)</a>]