CANNON BALL, N.D. >> With the federal government about to green-light the final phase of the Dakota Access pipeline, opponents of the project called today for protests around the world in an action they dubbed their “last stand.”

Some members of the Standing Rock Sioux tribe, which has been at the center of the debate for nearly a year, urged “emergency actions” via social media. The Indigenous Environmental Network told people to target fuel-transportation hubs and government buildings and to expect violence and mass arrests.

Protesters posted an online list of nearly 50 events in 23 states and the District of Columbia. In one early rally, several people were arrested for blocking public access to a federal building in San Francisco.

At a North Dakota encampment that has been the focus of the pipeline battle for months, the mood was tense, with a few dozen people milling about on a frigid morning and refusing to talk about their plans. They ordered an Associated Press reporter to leave.

The Army said Tuesday that it would allow the pipeline to cross under a Missouri River reservoir in North Dakota. That crossing is the last big chunk of construction. The official permission to complete the pipeline, known as an “easement,” could come as early as Wednesday.

The tribe maintains that the move will violate its treaty rights, and its attorneys have vowed to keep fighting in court.

In court documents filed Tuesday, the Justice Department said the Army intends to cancel further environmental study and allow pipe to be laid beneath Lake Oahe.

The Army is involved in pipeline approval under the river because the Army Corps of Engineers manages the river and its system of hydroelectric dams, which is owned by the federal government.

The 1,200-mile pipeline would carry North Dakota oil through the Dakotas and Iowa to a shipping point in Illinois. Construction is nearly complete but has been stalled while the Corps and Dallas-based developer Energy Transfer Partners battled in court over the final segment.

The Standing Rock Sioux tribe, whose reservation is just downstream from the crossing, fears a pipeline leak would pollute its drinking water. The tribe led protests last year that drew thousands of people who dubbed themselves “water protectors” to the encampment near the crossing. Protesters and police sometimes clashed, leading to nearly 700 arrests.

Energy Transfer Partners insists the pipeline will be safe.

The camp’s population has recently thinned to fewer than 300, and the Corps has notified remaining protesters that the government-owned land will be closed Feb. 22.

On Wednesday, police or pipeline security continued to monitor the camp from nearby hills, as they have done for months. In the camp, few people were outdoors, where the wind chill sank to minus 20 degrees. The tribe itself has told camp occupants to leave, though there has been no effort to remove them.

Chase Iron Eyes, an American Indian activist who has called on people to return to the camp rather than leave, encouraged that again in comments in a statement and on social media.

“I’ll see you on the front line,” said Iron Eyes, who is facing a felony charge for allegedly inciting a riot during protest action last week near the camp.

An assessment conducted last year determined the river crossing would not have a significant effect on the environment. However, the Army in December decided further study was warranted to address tribal concerns. The Corps launched a study on Jan. 18, but President Donald Trump signed an executive action six days later telling the Corps to proceed with construction.

The Army notified Congress on Tuesday that it planned to do so.

The pipeline builder is poised to begin drilling under Lake Oahe as soon as it has approval. Workers have drilled entry and exit holes for the crossing, and oil has been put in the pipeline leading up to the lake in anticipation of finishing the project. CEO Kelcy Warren has said the work could be done in about three months.