The current Rugby World Cup is likely to be the last featuring 20 countries, BBC Wales Sport can reveal.
An investigation for the Sport Wales TV show has learnt of plans to cut the tournament to 16 teams, with a second level tournament for so-called minnows.
The change is set to be discussed at a meeting of the International Rugby Board in Dublin in November.
The new format could be in place in time for the World Cup finals in New Zealand in 2011.
Twelve teams would qualify as seeds with the remaining four places to be determined through the second-level tournament.
Those games would be held a year before the main event with promotion and relegation between the tournaments in subsequent years.
"That's quite possible but not certain, we're reviewing everything," IRB head of communications Greg Thomas told Sport Wales.
"The main finals could stay at 20 or they could be cut to 16. We know what's working at the World Cup, but we are also looking at having 10 or 12 teams in a tournament the year before.
"That would give all qualifiers at least 12 months of preparation knowing that they will be playing in a World Cup.
"This year with the repechage, some sides didn't know they'd be in until six months before - that's not long enough, people must have a real chance to prepare."
But the suggested changes have provoked strong disapproval from countries such as Georgia, who have made a major impact at the current tournament.
If the plans go ahead they will kill rugby in a country like ours
Georgia coach Malkhaz Cheishvili
The Georgians almost created one of the biggest shocks in World Cup history last week before losing narrowly 14-10 to Ireland, and claimed their first victory in the tournament in thrashing Namibia 30-0 on Wednesday.
"If the plans go ahead they will be a very, very big mistake and will kill rugby in a country like ours," said Georgia head coach Malkhaz Cheishvili.
"We only have one chance in four years to play against the really good teams, so you can tell everybody that the Georgian delegation is strongly against the plans."
Any move to reduce the number of finalists is also likely to be resisted by more traditional "second tier" nations such as Japan, who made an unsuccessful bid to host the 2011 event.
"An easy solution seems to be less teams at the World Cup," said Japan coach John Kirwan, a World Cup winner with New Zealand back in 1987.
"But if you spend time with the players I'm with, it's the greatest experience of their life.
"You need to expand the game globally, and I think that we need to stay at 20 teams.
It's a complex jigsaw puzzle and we're going to take our time and do it properly, we have a commitment to the developing nations
IRB head of communications Greg Thomas
"If we spend some of the profits and make the tournament a week longer, I think that might solve some of the problems."
But Thomas believes a new format could increase World Cup revenue, which would eventually be ploughed back into the growth of the sport worldwide.
"Traditionalists will want the so-called minnows in the tournament," said Thomas.
"We understand that, but we also understand how important the World Cup is and that it continues to drive us commercially.
"That will ensure that we have money to give to the likes of Georgia, Fiji, Tonga, Madagascar, Ukraine, Ghana, Senegal and wherever else.
"It's a complex jigsaw puzzle and we're going to take our time and do it properly, we have a commitment to the developing nations."
*Watch the full feature on Sport Wales, BBC 2W, Thursday, 27 September, 2200 BST