The president of the Fiji Law Society was locked up overnight after urging judges not to accept commissions from the new regime.
Dorsami Naidu was being held in a Lautoka police cell after being interviewed by government representatives.
At the weekend he sent a letter to the country's judges - who were all sacked on Good Friday - asking them not to swear allegiance to Commodore Frank Bainimarama's Government.
Mr Naidu spoke to the Herald while in custody.
"It's just to teach me a lesson. So let them do that to me, we'll see what happens tomorrow."
Justice Ian Lloyd, one of three Appeal Court judges who ruled that Commodore Bainimarama's 2006 coup was illegal, said the crisis had left those in the legal profession in "invidious" positions.
The Australian-based Queen's Counsel left Fiji on Saturday after his sacking.
"This idiot Bainimarama is asking [judges] to sign up again and swear allegiance to an illegal regime. By law that is a treasonous act," he said.
"You can only judge with the law behind you. You can't judge for an illegal regime without compromising your own integrity."