The US House of Representatives has passed a provision allowing drilling for oil in Alaska's Arctic National Wildlife Refuge.
Opponents say the plan would threaten a key habitat for animals
The plan - backed by President Bush - will be debated by the Senate.
The provision was attached to a military spending bill that is set to be passed by the end of the year.
Supporters of the plan say the refuge offers an alternative source of energy to the Middle East, but opponents warn it would threaten the environment.
Republican Congressional leaders infuriated Democrats and environmental campaigners by adding the provision to a major defence bill.
Democrat Senator Frank Lautenberg called the move "a Christmas present for the oil industry".
Opening a portion of the refuge to oil and gas exploration has been a key objective of the Bush administration and a goal of US companies for a quarter of a century.
The White House believes access to the estimated 10bn-plus barrels of crude oil would cut American reliance on imports, create jobs and raise revenue.
The US has to import almost three out of every five barrels of oil it consumes.
But opponents say the plan would endanger a key habitat for migratory birds, polar bears, caribou and other animals.
Democrat senators have vowed to fight to the end to keep oil companies out of the Alaskan refuge.
Last month, the US Senate voted down an attempt to ban drilling in the area, which is the size of a small American state.