Native Americans and their supporters are rallying in Washington DC against continued construction of the disputed Dakota Access pipeline.
A federal judge this week declined to halt construction of the final section of the 3.8 billion dollar (£3.1 billion) pipeline, meaning oil could begin flowing through it as early as next week.
The Standing Rock Sioux and other tribes have tried to stop the pipeline, saying it threatens their sovereignty, religious rights and water supply.
The final, disputed section of the pipeline would pass under a reservoir which provides water to tribal reservations.
The pipeline itself is not on tribal land.
Protesters plan to march from the US Army Corps of Engineers headquarters to the White House in the US capital.
With the encouragement of US president Donald Trump's administration, the army has authorised construction of the pipeline to start again.
That move cancelled an environmental study ordered under the administration of former president Barack Obama.