The $3.5 billion Xayaburi Dam in Laos is one of 11 proposed dams for the Lower Mekong River that also flows through Thailand, Cambodia and Vietnam.

But environmentalists say the 1,280 megawatt dam will have far-reaching implications, especially in areas such as Vietnam's Mekong Delta region, prime rice growing country.

International Rivers, a U.S.-based environmental group, says 22,580 people from more than 100 countries signed a petition calling for canceling the project due to grave concerns about the future of the Lower Mekong basin.

The petition comes just a week before ministers of Mekong River Commission member states, Cambodia, Laos, Thailand and Vietnam, are to meet to make a final decision on the project.

The petition highlights concerns about the dam's impact, says Thailand campaign coordinator for International Rivers Pianporn Deetes.

"We would like the Mekong governments particularly the main players which are the Thai and Lao governments to be aware that the world is watching that there is a large number of people [who] would like to protect the Mekong River and livelihood of millions who depend on the Mekong River and would like them top make a good decision - not a decision that is based on politics."

Proposals for the 11 mainstream dams date back to 2006.  Under an agreement Thailand will purchase 95 percent of the electricity generated by the Xayaburi Dam.

Thailand's Energy Ministry says it has found no proof to back environmentalist claims of long-term damage on the river.  But Vietnam and Cambodian officials have backed environmentalists, saying it will severely harm fish stocks.

In April, the Lower Mekong river countries agreed to a suspend the dam's development pending further studies.  But recent reports point to ongoing construction at the site to the dam by Thai contractors.  

Carl Thayer, an academic at the University of New South Wales in Australia, says a decision by Laos to press ahead with the project will lead to diplomatic tensions.

"Both Vietnam and Cambodia even consulted, made statements they were quite concerned, both were very pleased to postpone it," says Thayer. "The first thing we have not said is the very strong remarks that would be made diplomatically to the Laos. And I think you might see some high level visits from Hanoi to Vientiane to please explain because [the dam] worked up a lot of concern."

Thayer says Vietnam would also look to countries which financially support the Mekong River Commission, including the United States, Australia and Japan, to apply diplomatic pressure on the Laos and Thai governments to further delay the project.

Analysts have called for a decade-long halt to the project to further assess the ecological and environmental impact from both the Xayaburi Dam development as well as further construction of dams along the Lower Mekong River system.

The Mekong River Commission ministerial meeting is scheduled to take place in Siem Reap, Cambodia on December 7.