Environmentalists and human rights activists are accusing Al Gore, the US vice-president and candidate for the Democratic party presidential nomination, of hypocrisy over his shareholding in an oil company prospecting in Colombian rainforests.
Mr Gore has targeted the environmental and human rights vote as part of his election campaign and was last week rated "the most knowledgeable" presidential candidate on green issues by the influential League of Conservation Voters.
But the U'wa Defense Working Group, which represents the U'wa indigenous tribe from the north east of Colombia, says Mr Gore is inextricably linked with Occidental Petroleum, the US oil group which plans to start drilling on its ancestral lands in the next few months in search of an estimated 1.5bn barrels of oil.
According to Mr Gore's official Public Financial Disclosure Report for 1998, the latest information available, the vice-president owned between $250,000 and $500,000 in Occidental stock inherited from his father, Albert Gore Sr, who died in 1998. Mr Gore Sr became a board member of Occidental Petroleum after losing his Senate seat in 1970.
Laura Quinn, a White House spokeswoman for Al Gore, said: "The stock was owned by his father and left in a trust of which he is executor. Most of the benefits go to his mother. Al Gore is not on the board of directors and does not have any special influence over the company. The connection to Occidental is indirect and has been longstanding."
According to the Centre for Public Integrity, a non-profit organisation that analyses ethics in politics, Ray Irani, the Occidental chief executive, made a donation of $100,000 to the Democratic National Committee in the early 90s following a stay in the Lincoln Room of the White House. The campaign group is urging environmentalists not to vote for Mr Gore and to protest about his links to Occidental on the campaign trail.
Stephen Kretzmann, U'wa campaign co-ordinator for Amazon Watch, a California-based environmental group, said: "This will not look good for Al Gore in the midst of an election campaign. It is clear that he could stop the drilling with a phone call and if he doesn't do something about this he will lose the environmental and human rights vote."
The U'wa, who number 5,000, first hit the headlines in 1996 when they threatened to commit collective suicide if Occidental's drilling plans were not halted.
The drill site falls 600m outside the legally recognised U'wa Unified Reserve but the tribe claims it is within larger, traditional ancestral territory.
The UDWG claims development of the site would be damaging to the tribe and the environment because of the likely increase in oil-related violence between different armed factions in the politically unstable region.
It says Occidental's existing pipeline has been attacked more than 600 times in the last 12 years leading to 2.1m barrels of crude oil spilling into the soil and rivers, and that U'wa members and humanitarian workers have been killed or injured in the cross-fire.
Occidental said earlier this month that it planned to start building roads to the test site at the end of January and would sink the first test well at the site in May.
Ken Hufmann, Occidental's vice-president of investor relations, refused to comment on Mr Gore's stock holding in the company or any political donations that it had made.
He would say only: "We're moving ahead with plans to drill the well but I have no specific dates."