Loghman Sawari, who is 21, fled to Fiji from Papua New Guinea's Manus Island.
He and his lawyer were on their way to meet with Immigration in Suva on Friday to seek asylum when he was stopped by police and put on a plane back to PNG.
Amnesty's Pacific Researcher, Kate Schuetze, said Fiji had failed an important test at a time when it's making a bid for a seat on the UN's Human Rights Council.
"The Fijian authorities gave assurances that he would not be arrested before he had that interview."