The medical charity Doctors Without Borders says it has refused to comply with Nauru government orders to hand over medical records.
The charity, also known as Médicins Sans Frontières, was last week made to leave the island, where it had been providing mental health care for refugees and locals.
In a statement, the charity's Operations Director, Marc Biot, said Nauru's Supreme Court also ordered it to transfer its patients' files to the Ministry of Health.
Dr Biot said that to comply with the orders would entail a breach of patients rights, as there would not be enough time to secure their consent.
Instead the charity had ensured that only patients would be able to access their files, he explained.
He said Médicins Sans Frontières complied with orders to delete all its copies of medical files.
"It was clear to us that our patients' health and continuity of care was of little concern to the health authority during this process," said Dr Biot.
"We have reminded the Ministry of Health that they can only use this information to ensure the best care for patients and that this information is protected by medical confidentiality."