A former secretary of justice in Nauru, David Lambourne, says passports cannot be withdrawn on the basis of alleged past conduct.
20 Nauruans who have been accused of involvement in an anti government protest last year have had their passports withdrawn.
Among them are three former MPs, including former president Sprent Dabwido, who is in urgent need of cardiac medical care that is not available in Nauru.
Nauru is yet to announce the reasons for the cancellations, though it is a device it used last year to detain then MP Roland Kun for more than 12 months.
Mr Kun escaped from the island using a New Zealand passport after he had been given New Zealand citizenship.
Don Wiseman asked Mr Lambourne what he thought the Nauru government was trying to achieve.