The largest tribe in South Dakota told the state’s governor on Thursday that she is “not welcome” in its homelands, a sprawling reservation southwest of the capital city Pierre.

The extraordinary step is the latest escalation in a years-long feud over the controversial Keystone XL oil pipeline, a conflict that now pits advocates of indigenous rights, environmentalism and free speech against the state government, the Trump administration and a powerful oil company.

The Oglala Sioux Tribal Council voted to ban Gov. Kristi L. Noem (R) from its Pine Ridge Reservation on Wednesday and sent her a sharply-worded letter on Thursday.

“If you do not honor this directive,” wrote the tribe’s president, Julian Bear Runner, “... we will have no choice but to banish you.”

In response, Noem’s spokeswoman said the governor was surprised at the letter but said she will “maintain her efforts to build relationships with the tribes.”

Bear Runner pledged that the ban would last until Noem rescinds her support for a pair of laws the state passed in response to promised demonstrations against the Keystone XL pipeline project. The laws, which codify “riot boosting,” are designed to prevent protests that may disrupt pipeline construction.

Critics say the legislation was designed to prevent the sort of large-scale, high-profile protests that unfolded over the Dakota Access pipeline in neighboring North Dakota, which began in 2016 and lasted for months. Demonstrations there led to more than 750 arrests, and the policing effort cost the state $38 million.

Noem announced the bills in the waning days of the year’s legislative session, and the state’s Republican majorities pushed them through the House and Senate in just 72 hours.

“My pipeline bills make clear that we will not let rioters control our economic development,” Noem said in a statement after she signed the bills into law in late March.

But the Oglala Sioux Tribe, the American Civil Liberties Union and other advocacy groups have staunchly opposed the new laws, criticizing what they see as serious threats to free speech.

Together, the laws would allow officials to sue activists if violence or law breaking occurs at a protest they organized, promoted or somehow encouraged. Money collected from those lawsuits would be used to pay for damage claims stemming from that demonstration or for law enforcement costs.

The ACLU filed a federal lawsuit challenging the new statute (and two existing criminal riot laws), claiming that they are too vague, too broad and impinge on protected speech.

“We believe they chill free speech and they are therefore unconstitutional,” said Courtney Bowie, the legal director for the ACLU’s South Dakota chapter, in an interview with The Washington Post. “I don’t think anyone can accurately define what ‘riot boosting’ is ... the law is completely unclear and that’s part of the problem.”

Chase Iron Eyes, the public relations liaison for Bear Runner, told The Post that the laws pose a direct threat to members of the Oglala Sioux Tribe, many of whom plan to oppose the pipeline project, which would run through, and could threaten, sacred tribal lands.

“We have a right to speak freely,” Iron Eyes said. “We have a right to peaceably assemble."

Tribe leaders have said Noem and state legislators excluded them from the bill crafting process and instead elected to meet with TransCanada, the company behind the $8 billion project. Iron Eyes said the effort amounted to a violation of the tribe’s sovereignty and the treaty it signed with the United States.

“We don’t feel Kristi Noem wrote this legislation for the good of South Dakotans, or our land, or our water,” he said. “We believe big extraction wrote this legislation.”

The tribe’s response on Wednesday was an unprecedented step, said Iron Eyes, who couldn’t recall another instance when leaders told a representative of state government that she wasn’t welcome on their land. If Noem violates the resolution, she could face banishment, a serious formal tribal process — though Iron Eyes said he doesn’t think it’ll come to that.

Noem’s press secretary, Kristin Wileman, said in a statement that the governor “has spent considerable time in Pine Ridge building relationships with tribal members.”

“This announcement from Oglala Sioux tribal leadership is inconsistent with the interactions she has had with members of the community,” Wileman said.

Noem visited the reservation in March, as residents were recovering from severe flooding in the region, a trip leaders welcomed at the time. However, Iron Eyes said, she made subsequent trips to the reservation without informing Bear Runner or other leaders, which, he said, was a lapse in diplomatic courtesy.

“It’s unfortunate that the governor was welcomed by Oglala Sioux’s leadership when resources were needed during recent storms, but communication has been cut off when she has tried to directly interact with members of the Pine Ridge community,” Wileman said.

The letter is another sign of further fraying relationships between the state government and its neighboring tribes in the weeks since Noem proposed the protest bills. In mid-March, four tribal chairmen, including Bear Runner, asked the state not to display their flags at the Capitol, saying that the bills had “destroyed our trust” in South Dakota’s leadership.

But Iron Eyes said he’s confident the laws will be struck down — eventually.

“We’re on the right side, here, of spirit and morality,” he said. “And the legality just needs to come along. We’ve got to evolve.”

From the Oval Office, however, President Trump has tried to muscle the pipeline project through its court challenges. Days after Noem signed her bills into law, Trump signed an executive order in an attempt to clear a path for pipeline construction. That, too, now faces legal challenges.