Environmentalists in Ecuador say they have collected enough signatures to have a referendum on whether the Yasuni National Park in the Amazon should be opened to further oil exploration.
They said 727,947 people had signed their petition to have a vote - more than required by Ecuadorian law.
President Rafael Correa has promised that any oil earnings from the park would be used for poverty alleviation.
But critics say one of the world's most biodiverse areas would be damaged.
The signatures were gathered by Yasunidos, an organisation of environmentalist and indigenous groups.
"With these signatures we are certain that the popular consultation vote will go ahead," Carla Espin of Yasunidos told reporters in the Ecuadorian capital, Quito.
The signatures, which came from as far away as Australia, Mexico and Europe, still need to be validated by the Ecuadorian electoral authorities.
It would then be up to the Constitutional Court to authorise a referendum on the issue.
Conservation plans ditched
Limited oil exploitation has been taking place in parts of Yasuni, which covers nearly 10,000 sq km (3,860 sq miles), since the 1970s.
But last year President Rafael Correa abandoned a conservation plan that would have seen rich nations pay Ecuador not to drill in previously untouched parts of the park.
Mr Correa said the initiative had attracted only a fraction of the $3.6bn (£2.1bn) it had aimed to raise, leaving Ecuador with no choice but go ahead with drilling. Oil is the country's main export.
There were protests in Quito against his decision.
The park supports a huge variety of wildlife, including unique species of birds, monkeys and amphibians.
It is also home to the Huaorani and other indigenous people who had virtually no contact with the outside world until recent decades.
Yasuni oilfields hold an estimated 846 million barrels of crude, 20 percent of Ecuador's reserves.