After a tortuous 'Will-she-or-won’t-she' over the Keystone XL pipeline, Hillary Clinton is facing a different pipeline headache that pits some of her own allies against each other, presenting her with a possible lose-lose political dilemma.

Controversy has been brewing for months over the Dakota Access Pipeline, which would transport crude oil from fields in North Dakota across four states. Tensions came to a head in recent days with violent clashes between police and protesters trying to block the pipeline’s path, ratcheting up the pressure on Clinton to take a side.

Clinton, who weighed in on the Dakota Access pipeline for the first time last week in a noncommittal statement, finds herself torn between labor unions on one side, who want the jobs created by the project, and Native American activists and environments on the other side, who say the pipeline would pollute water and violate sacred land.

“If Clinton thought Keystone was bad, get ready for Dakota Access. This is an issue that is not going away,” said Jamie Henn, a co-founder of the environmental group 350 Action, which has endorsed Clinton and is canvassing members to help get her elected. “She's triangulating and you shouldn't triangulate on issues of social justice.”

The pipeline, which is already under construction, would come within a half mile of the Standing Rock Sioux reservation, where tribal activists have been resisting it since April.

On Thursday, activists erected a teepee in the lobby of Clinton’s campaign headquarters in Brooklyn as part of a protest designed to pressure her to oppose the pipeline. And on Sunday, Our Revolution, the group that grew out of Bernie Sanders' presidential campaign, started a petition calling on Clinton to kill the pipeline, even as Sanders campaigns for the Democratic nominee.

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“There is one person who will have the power to stop the Dakota Access Pipeline: Secretary Hillary Clinton. If she is to be our next president, she will have the power to stop the pipeline. And our best opportunity to get her to oppose it is before the election,” the petition read.

Sanders also joined a protest outside the White House against the pipeline and has formally requested President Obama intervene in the situation.

Unlike Keystone, which crossed an international border, the Dakota Access Pipeline does not require a presidential permit. But opponents are calling on Obama, and Clinton if she wins, to revoke permits issued by the Army Corps of Engineers and implement a more thorough environmental and tribal review process.

Meanwhile, on the other side is not just Energy Transfer Partners, the Dallas-based company behind the $3.7 billion project, but many labor unions that have been key allies of Clinton and other Democrats. (According to his financial disclosure forms, Donald Trump, the Republican nominee for president, has close ties to the pipeline through his investment in Energy Transfer Partners, whose CEO has donated more than $100,000 to Trump's campaign.)

The AFl-CIO, the union umbrella organization that represents millions of workers, came out in favor of the pipeline in September.

“Pipelines are less costly, more reliable and less energy intensive than other forms of transporting fuels, and pipeline construction and maintenance provides quality jobs to tens of thousands of skilled workers,” said AFL-CIO President Richard Trumka.

Support inside the labor movement has been led by the Laborers' International Union of North America, whose president, Terry O’Sullivan, sent a scathing letter to members last week excoriating the handful of unions that have spoken out against the pipeline.

“Some of our so-called brothers and sisters in the trade union movement have abandoned solidarity with the working class and are instead throwing in with environmentalists who have co-opted the tribes in their effort to fight pipelines,” O’Sullivan wrote. “LIUNA will not forget the reprehensible actions.”

The defecting unions — whom O’Sullivan called “bottom-feeding organizations” — include major groups that represent a newer breed of labor, based more around the service industry than skilled trades, like the Service Employees International Union and the Communications Workers of America.

All have endorsed Clinton.

Emails stolen by hackers and released by Wikileaks show Clinton officials were worried about losing O’Sullivan’s support earlier this year when Clinton came out against a different pipeline in New Hampshire.

“Terry is considering pulling back on the campaign and is cancelling his Las Vegas trip” on behalf of the campaign, Labor Outreach Director Nikki Budzinski warned colleagues in February.

Budzinski requested Clinton personally spend 10 minutes one-on-one with O’Sullivan to “smooth some things out.” “He just needs assurances of her energy policy proposal,” Budzinski added.

It’s unknown if she did. But on the Dakota Access Pipeline, Clinton so far seems to be biding her time.

"Now, all of the parties involved — including the federal government, the pipeline company and contractors, the state of North Dakota, and the tribes — need to find a path forward that serves the broadest public interest," campaign spokeswoman Xochitl Hinojosa said in Clinton’s only major public remarks on the pipeline last week. "As that happens, it's important that on the ground in North Dakota, everyone respects demonstrators' rights to protest peacefully, and workers' rights to do their jobs safely."