All EU member states have signed and ratified the Montego Bay Convention on the Law of the Sea.

Omissions

• The claim omits that, alongside all 27 member states, the European Union itself is a separate party to UNCLOS (via Annex IX), which reinforces rather than weakens the statement.
• Some EU member states became parties by accession/succession rather than through the classic sign-then-ratify sequence, though all are fully bound as parties.

Sources

• PrimaryUnited Nations Treaty Collection — UN Convention on the Law of the Sea (Montego Bay, 10 December 1982)STATUS AS AT: 12-10-2026 ... CHAPTER XXI LAW OF THE SEA ... 6. United Nations Convention on the Law of the Sea, Montego Bay, 10 December 1982 ... Status Signatories: 157. Parties: 172. The entry also records the European Union's instrument of formal confirmation and the declarations of EU member states such as Greece, which notes that as a State member of the European Union it has transferred jurisdiction over certain matters to the EU.
• PrimaryInternational Seabed Authority — The United Nations Convention on the Law of the Sea at 40As of July 2021 it has been ratified by 168 parties, which includes 167 States (164 United Nations member States plus the UN Observer State Palestine, as well as the Cook Islands and Niue) and the European Union. All parties to UNCLOS are automatically members of ISA. An additional 14 UN Member States have signed it, but not ratified it.
• PrimaryInforMEA — Parties to UNCLOS (UNEP information portal)Party list includes EU member states such as Finland, France, Luxembourg (which notes it is a member of the European Community), Spain, and others, each recorded with ratification dates under the United Nations Convention on the Law of the Sea.