HOUSTON -- A movement protesting the construction of a major oil pipeline by TransCanada has posted a video online asking the presidential campaign candidates to withdraw the support for the project that they voiced during this week's debate.

The group is also soliciting signatures for an "open letter" requesting that the two campaigns turn away from the controversial Keystone XL pipeline, including the southern leg that's currently being built from Cushing, Okla., to the Texas Gulf of Mexico coast.

Activists are upset over comments that Mitt Romney and President Obama made during a Tuesday night debate at Hofstra University. Both candidates said they supported pipelines to deliver more Canadian oil to U.S. markets (EnergyWire, Oct. 17).

Though TransCanada has yet to receive State Department approval to build a pipeline across the U.S.-Canada border, the company is proceeding with the southernmost extension of the line. A TransCanada spokesman said the new pipeline should come online late next year.

Booming crude production out of new tight and shale oil fields in the West and Midwest has led to a glut of supply at a massive storage complex at Cushing. Pipeline reversals and new lines are being sought to increase the flow of oil from Cushing to Houston-area refineries to lessen the glut.

But in a three-and-a-half-minute video posted on YouTube, activists running the Tar Sands Blockade movement argue that the pipeline is an environmental disaster waiting to happen. In it, they compare Keystone XL to a pipeline run by Enbridge that ruptured and leaked oil into Michigan's Kalamazoo River.

The heavier bitumen-based crude is more corrosive and poses a greater risk of pipeline leaks, as shown by a series of leaks on an earlier pipeline built under the Keystone project, opponents say. They also argue that Keystone XL would encourage further development of Canada's oil sands, thereby exacerbating the climate change problem.

The first segment of the Keystone system, a line that carries 591,000 barrels a day to Patoka, Ill., was temporarily shut in Thursday after TransCanada reported discovering problems with the line. New crude shipments along the line are expected to be delayed until the company can perform maintenance work.

The new online "planetary service announcement" purportedly shows actress Daryl Hannah in action at a recent protest in northeastern Texas. Hannah was arrested and spent a night in jail as a result of her activism there.

"When a law is unjust, sometimes as a last resort, the only option is to break it," Hannah said in a statement shortly after her release.

The Tar Sands Blockade is gathering support from other environmental groups and activists. Earlier this week, the group announced that 50 supporters trespassed onto private land and TransCanada's easement in a show of solidarity with protesters who have been manning a tree encampment for nearly a month.

The group boasts that the walk-on protest is "the largest yet attempted in the history of protests surrounding Keystone XL construction." The group has vowed to continue the tree protest indefinitely, though TransCanada has said it has rerouted work around the tree sit-in to avoid injury to the protesters.

TransCanada maintains that the oil Keystone XL will carry isn't substantially different from the oil delivered by thousands of miles of other pipeline networks across the country. A past study by the Council on Foreign Relations concluded that the oil sands projects' contribution to climate change was minimal compared with other sources of carbon dioxide pollution.

Tar Sands Blockade's latest video can be found here.