The Valero refinery looms on the horizon in Port Arthur Texas. Port Arthur, Texas is the end of the line for oil that would travel through the proposed Keystone XL Pipeline. (Michael S. Williamson/THE WASHINGTON POST)

Keystone XL pipeline foes have tried petitioning the government, grabbing media attention and filing lawsuits. Now, with the southern leg of the pipeline under construction, they’re turning to civil disobedience — and actress Daryl Hannah.

On Monday, after a weekend of nonviolent civil disobedience training, supporters of the Tar Sands Blockade rallied in Winnsboro, Tex., where protesters were holding a “sit-in” 70 feet off the ground in a swath of trees. The trees stand in the middle of a corridor already cleared for the pipeline. The tree-climbing pipeline foes unfurled a banner that reads: “Rise Up and Defend Your Homes.”

Although the permit for the northern leg of the Keystone XL pipeline is still under consideration by the State Department, the southern leg of the pipeline has won the support of President Obama, obtained permits from the Army Corps of Engineers and turned back challenges in Texas courts.

Landowners and activists such as Hannah are trying to physically stand in the way of the equipment that is laying down the pipeline. One day, people chained themselves to a truck. Another day, they stood in front of bulldozers. Several people have been arrested, including, briefly, a New York Times reporter.

The blockade group said 10 people were arrested Monday after locking themselves to pieces of heavy equipment. Earlier in the month, Hannah joined east Texas landowner Eleanor Fairchild to protest TransCanada’s Keystone XL pipeline. On Oct. 4, they were arrested on charges of criminal trespassing for standing in front of excavation equipment on Fairchild’s property.

The Tar Sands Blockade says civil disobedience is justified and that Obama’s March endorsement of the southern leg of the pipeline was a “last straw.” It accuses local police of excessively rough treatment of protesters.

“The evidence was clear . . . that people had done everything to use institutions to expose the fraud and malpractice of this corporation and that they had been ignored, even by Barack Obama,” said Ron Seifert, spokesman for the Tar Sands Blockade. “The logical thing to do was to rise up and protect your homes.”

But TransCanada, which obtained a temporary restraining order from a Texas district court, says protesters are trespassing.

“The right-of-way is an active construction site and only authorized personnel are able to go on this area,” TransCanada spokesman Shawn Howard said in an e-mail. “It is important to us that all of our work sites are safe and our workers go home safe each and every day.” Howard added that “while construction is underway, the agreement we sign with the landowner does permit us to restrict access to that area.” He said that journalists had refused to show credentials and that some “professional activists” had been posing as journalists.

The small Tar Sands Blockade group has drawn support from other critics of the pipeline, which would carry heavy crude oil from Canada’s oil, or tar, sands across the Great Plains to the Texas Gulf of Mexico coast.

“Peaceful and nonviolent civil disobedience is one tool in the activist toolkit,” Bill McKibben, a Middlebury College professor who has been one of the leading foes of the Keystone XL, said in an e-mail. “You don’t want to use it all the time because it gets dull. But this is the kind of case for which it’s designed, when you’re up against the wall and truly powerful forces are refusing to listen to reason and just pushing ahead regardless.”

“The only option afforded to powerless individuals who have been abused by the system is this tactic of nonviolent civil disobedience,” said Seifert, the Tar Sands Blockade spokesman. “Everything has been done to petition for justice at every level. And the institutions failed. This is a clear case of injustice, and it’s up to people to rise up and defend themselves.”

Even among environmentalists, there is skepticism that a small number of activists can stop the southern leg of the pipeline at this point. But Seifert said he hoped the protests might attract national support and that the pipeline’s foes might still prevail in remaining court cases, including one filed by Texas rice farmers and an appeal by Julia Trigg Crawford, a family farm manager in north Texas.

“We’re not naive either,” Seifert said. “A handful of people on a day-to-day basis are not going to stop the Keystone XL. We’ve seen what a massive operation this is.”

One person missing from the protests is David Daniels, who has been featured in major media stories for opposing the pipeline. Daniels had signed an agreement with TransCanada in 2010 that he later regretted. “If that means I’ll have to stand in front of a bulldozer, I’ll stand in front of a bulldozer,” he told NPR in August.

But TransCanada filed a lawsuit against him for breach of contract, which in Texas means Daniels would have to pay TransCanada’s legal fees if he lost the case. So, Daniels recently agreed to comply with the 2010 terms. When protesters came to his property in Winnsboro, he asked them to leave, and they did.

“David was kind of the show pony,” his attorney, Norman Ladd said. “We have fought the fight that we can fight. Now, it is time for us to look at the big picture and settle our claim.”