The boat was seized on the southern Italian island and fined under a draconian security decree drawn up by outgoing interior minister Matteo Salvini.
Charity Mediterranea Saving Humans said the ship was impounded after “entering [Italian] territorial waters with the authorisation of the competent maritime authorities”.
The collective of mainly left-wing Italian activists tweeted: “Our captain and the ship's owner were notified of the administrative seizure of Mare Jonio along with a fine of 300,000 euros for violating the security decree.”
In a statement, they called it an “absurd and inhuman” application of the law.
? #MareJonio: assurda e paradossale applicazione Decreto Sicurezza Bis, sequestro nave e multa da 300mila euro.
Nostro comunicato ?https://t.co/mEHmONHHBH
— Mediterranea Saving Humans (@RescueMed) September 3, 2019
The last 31 rescued migrants on board were disembarked shortly before the seizure, the charity said.
The Mare Jonio rescued 98 people off the coast of Libya last week and 67, including women, children and the sick, have already been disembarked in Italy.