A man takes part in a march with veterans to Backwater Bridge just outside of the Oceti Sakowin Camp during a snow fall as "water protectors" continue to demonstrate against plans to pass the Dakota Access pipeline adjacent to the Standing Rock Indian Reservation, near Cannon Ball, North Dakota, December 5, 2016.

Activists are threatening "mass resistance" to President Donald Trump and the Army Corps of Engineers on the hotly disputed Dakota Access pipeline — and it could be difficult for the White House to counter the movement.

Acting on an order from Trump, the Army Corps of Engineers on Tuesday said it would grant the easement that Energy Transfer Partners needs to finish the final stretch of the pipeline. It also canceled an environmental review the Corps said it would undertake while President Barack Obama was still in office.

That announcement amplified alarm among Native Americans and their allies, who oppose the pipeline because it would pass beneath Lake Oahe, a drinking water source and sacred site.

"The granting of an easement, without any environmental review or tribal consultation, is not the end of this fight — it is the new beginning. Expect mass resistance far beyond what Trump has seen so far," the Indigenous Environmental Network said in a statement.

What that resistance will look like is uncertain. The movement appears to be taking on a diffuse, leaderless structure, similar to Occupy Wall Street and Black Lives Matter. Such movements tend to have staying power.

Dakota Access pipeline route, source: Energy Transfer Partners



On the one hand, the Standing Rock Sioux Tribal Council, whose reservation is half a mile south of the contested site, is mounting a legal challenge to the easement and promoting a march on Washington next month.

Standing Rock Tribal Council Chairman Dave Archambault II asked protesters to return home after the Army Corps of Engineers announced it would not grant the easement in December. He repeated that request again on Tuesday.

But other councils and camp organizers have sent conflicting messages, suggesting the chairman may not be able to control the flow of activists to the region.

The Cheyenne River Tribal Council of South Dakota invited a limited number of volunteers from the former servicemember group Veterans Stand to return to Standing Rock, Anthony Diggs, secretary of communications for the group, told CNBC.

U.S. military veterans associated with the group are on site assisting with clean up and other logistics. The group is currently forming a network that can deploy thousands of veterans to Standing Rock as needed, but stresses it will only do so in consultation with tribal leaders.

"Our plan is to send support where support is needed, and in light of the easement being granted over the next few days, we'll be able to better determine where that will be," Diggs said.