The 33-year-old man, who is being held in the Wickham Point Immigration Detention Centre near Darwin, refused to eat after being denied refugee status.
Human rights lawyer Steven Blanks said there was legislation in place that would allow authorities to save the man's life.
"It authorises the Department of Immigration to direct doctors to provide medical treatment against the consent of asylum seekers where that medical treatment is necessary to preserve their life or health," he said.
The Iranian man has given written instruction that he must not be revived if he loses consciousness.
But Mr Blanks said international standards specify medical treatment should be used, even if an asylum seeker had refused it.
Source: Yahoo 7 News, 20/12/15