Daryl Hannah is hardly the first movie star to take a stand in social activism, but she's clearly among the most committed to her cause.

The "Splash" and "Kill Bill" actress was arrested not once, but twice, for taking part in protests against the expansion of the Keystone XL Pipeline, a controversial crude oil transportation system that extends from Alberta, Canada to the Gulf Coast of Texas, with a final and fourth phase still pending government approval.

Hannah puts her money where her mouth is as an executive producer on the new documentary, "Above All Else," which premieres tonight at the SXSW Film Festival and follows the story of a landowner in East Texas who organizes a "tree sit" to halt the pipeline's construction because of both environmental and eminent domain concerns.

"It's not something that you want to do but it's definitely something I'd be willing to do, yeah," Hannah told Yahoo Movies when asked if she'd risk yet another arrest. "I'm now one of over 80,000 people who have committed to civil disobedience if and when it comes to it -- to risk arrest or pledge to risk arrest. There's about 80,000 people who have signed on to participate in civil disobedience if there's any further progress on the Keystone."

[Related: Daryl Hannah Arrested (Again); Sean Hannity Promises Her Bail Money]

Hannah, along with fellow environmental activist Julia Butterfly-Hill, was approached to support the film because director John Fiege "was aware that we were planning to go down to give some physical and actual tangible support to the people who were struggling against the southern route of the Keystone pipeline," she said.

"I believe in terms of the human aspect of what people are going through on the ground, John has done a beautiful job of showing the people who are being affected by this -- people of all walks of life," Hannah said about the documentary.

"Eleanor [Fairchild], who I was arrested with who was featured in the film, she comes from an oil family, her husband hunted oil, so she knows a lot about oil and doesn't have issues with a normal pipeline necessarily going across her property. But she has a farm and she has springs and she was very concerned about the idea of tar sands coming through there. Also I think everybody who had to suffer the eminent domain abuses had extremely devastating experiences -- devastating to their families, devastating to the investment that they've put into their properties and their future."

The film captures not only the thorny issue of eminent domain in Texas, but also the effects it's had on subjects like Fairchild. "They were burning the trees, they came in the middle of the night, they broke the fence," Hannah said. "And they would tell her that they were watching her -- scary things for an 89-year-old woman."

"Above All Else" marks the second social justice documentary that Hannah has executive produced in as many years, after last year's climate change expose "Greedy Lying Bastards." The actress-turned-activist, however, has shot, directed, and produced a number of shorts on sustainability and clean energy, and considers herself one of the very first "video bloggers" on the internet for a series she did on the subjects over a decade ago.

[Related: How a 'Splash' Joke Led to the 'Madison' Baby Name Boom]

Of course it was the headline-grabbing arrests that brought Hannah's efforts the most attention, and landed her on talk shows, including one particularly spirited debate with FOX News's Sean Hannity.

"It definitely helped bring awareness," Hannah said. "That's the benefit about practicing civil disobedience, that it can grab the attention of the media and then make people maybe pay attention a little bit more."

The Keystone XL Pipeline is approaching a critical juncture with President Obama expected to make a decision on the final phase "within a matter of months," according to the filmmakers.

Follow Kevin Polowy on Twitter