Fiji will be suspended from the Pacific Islands Forum if it does not set a firm election date for this year and present a clear and detailed timetable for doing so before May 1.
The Pacific Forum leaders unanimously laid down the ground-breaking deadline after meeting for four hours in Port Moresby yesterday.
The suspension will mean Fiji cannot attend meetings between forum leaders, ministers or officials.
It will also be excluded from benefiting from any regional initiatives run under the forum and - similar to a Commonwealth suspension - cannot receive any technical assistance beyond what was needed to help it hold elections.
Prime Minister John Key said it sent a "strong message" to Fiji.
"It solely comes back to whether Frank Bainimarama truly wants to restore democracy. If he does, this is a way through," he said.
Both Mr Key and forum chairman Toke Talagi said the decision was made by consensus - despite concern beforehand that the forum would be split with the Melanesian countries wanting to go easy on Fiji while Australia and New Zealand wanted a harder line.
"I do think it's hard enough. It's a clear, direct message, and one that Fiji can comply with if it has the political will to do so," Mr Key said.
To escape suspension, Fiji's interim government will have to provide a timetable for elections that has the buy-in from other political stakeholders, reached "without threats, preconditions, ultimatums, predetermined outcomes".
It also has to commit to sending the military back to the barracks after the election, and for it to submit to the authority of an elected government.
Australian PM Kevin Rudd said it sent a "loud and clear message" from all countries in the region that Fiji's military regime must return to the ballot box and send its soldiers back to the barracks.
PNG PM Sir Michael Somare - who has worked closely with Commodore Frank Bainimarama - said he also endorsed the decision, despite earlier releasing his speech to the media, which called for Fiji to escape punitive measures.
Mr Key said smaller states such as Kiribati and Tuvalu, which partly relied on Fiji economically, had also been assured that if there was retaliatory action for the decision, other forum countries would step in to help.
It is a landmark decision for the Pacific Forum, which has never had to consider disciplinary action against a member state.
However, it is likely to anger Commodore Bainimarama - and could push him to carry through with threats made after the forum meeting last year that he would pull Fiji out of the forum rather than face suspension.
Under the Biketawa Declaration, the leaders had an open slate on what they could do with Fiji.
The declaration does not specify any actions to discipline recalcitrant states, leaving it to the leaders to decide what measures are suitable.
Commodore Bainimarama pulled out of the meeting last week, saying he was needed in Fiji to focus on the aftermath of the floods - a decision criticised by both New Zealand and Australia.
Interim Attorney-General Aiyaz Saiyed-Khaiyum represented Fiji at the meeting. Afterward, he said he had not given a time frame for elections, but had clarified what he said were misunderstandings about the process Fiji was undertaking.
The day before the meeting, Commodore Bainimarama spoke to military personnel, telling them Fiji would move toward elections in its own time and he did not care if it took five to 10 years.
In the past week, Commodore Bainimarama has also sacked his foreign affairs secretary after he commented on Commodore Bainimarama's decision not to attend the forum.