WASHINGTON - A Canadian woman was among as many as 50 environmental activists handcuffed and taken to jail Sunday on the second day of peaceful White House protests against TransCanada's controversial Keystone XL pipeline.

Fifty protesters were already in a downtown D.C. jail following their arrests outside the White House on Saturday, the opening day of a two-week civil disobedience campaign. They're expected to be released late Monday after being processed at police headquarters.

By noon on a steamy Sunday, police began arresting more demonstrators, including 68-year-old Patricia Warwick of Toronto. A 65-year-old woman from Massachusetts who's celebrating her birthday was also lead away in handcuffs from a stretch of sidewalk outside the White House.

All of those arrested on Sunday were later released, said Sgt. David Schlosser, an official with the U.S. Park Police. He added that Saturday's activists have been held in jail for reasons that could include inadequate ID or previous arrests.

All of those arrested, however, are facing charges of failing to obey an order governing protests on the sidewalk, he said.

For the second day running, the protesters _ some of whom held signs that read: "Obama Will You Stand Up To Big Oil?" _ were asked to vacate the sidewalk by police. When they refused, they were arrested one by one and taken to the central cell block of the city's police department.

Officials for Tars Sands Action, the group that has organized the two-week campaign, have been taken aback by the fact that activists are spending days in jail. They say police originally assured them protesters would be released after being warned and fined.

"We've been told now that they're doing it as a deterrent," spokesman Daniel Kessler said.

The Martin Luther King Jr. memorial is going to be unveiled on the National Mall on Saturday, and police want to get the message across that they don't want the Keystone protest to mar those festivities, he said.

"Which is ironic because these are peaceful demonstrations, and exactly the type of protests that Martin Luther King advocated," Kessler said.

Obama will decide by the end of the year whether to allow Calgary-based TransCanada (TSX:TRP) to build the US$7 billion pipeline. It would transport millions of barrels of Alberta oilsands crude a week through the American heartland and to Gulf Coast refineries.

Opponents say Keystone is an environmental disaster waiting to happen, pointing to a number of recent spills along pipelines. They also oppose Alberta's oilsands due to their high greenhouse gas emissions. Advocates, meantime, say the pipeline will create thousands of American jobs amid a lingering recession, and will also help end U.S. dependence on Middle Eastern oil.

One Canadian activist at the protest on Sunday said she hoped the event would draw further attention to the pipeline controversy in the United States.

"I definitely feel like this is a moment where we can highlight this issue in the general public, in particular in the U.S.," said Heather Milton Lightening, an Alberta activist who's part of a group called the Indigenous Environmental Network.

"For us, it's an issue of importance to get community voices heard because they are the ones who are most impacted. When it comes to First Nations in Canada, many of the communities ... are dealing with drilling, open-pit mining, they're dealing with infrastructure on their land."

She added the Keystone XL would traverse "a huge amount of land. There are many sacred sites it's going to pass through .... the tarsands don't make sense, but the pipelines make even less sense."

People from across the U.S. participated in Sunday's event, including a group of doctors from Chesapeake Physicians for Social Responsibility. They wore white lab coats as they stood at a White House gate and awaited arrest.

Obama hasn't been in Washington to take in the protests; he's vacationing with his family in Martha's Vineyard. But the activists are vowing they'll still be outside 1600 Pennsylvania Avenue when he returns late next week.

Jamie Henn, one of the event's organizers, says as many as 100 people were expected to attend a training session on Sunday night to prepare for Monday's sit-ins, including a group of Nebraska farmers and ranchers.

Keystone XL has become a lightning rod for the U.S. environmental movement in the wake of failed climate change legislation once passionately promoted by the president. Several opponents of the project, including jailed U.S. enviromentalist Bill McKibben, have pointed out that the pipeline decision is one of few the president can make that does not require congressional involvement.

"Saturday's arrests and overnight jailings are already lighting a fire," Mike Tidwell, director of the Chesapeake Climate Action Network, who was also arrested Saturday, said in a statement released by Tar Sands Action.

Tidwell was released Saturday night.

"More people are now inspired, determined, and committed to join," he said. "Word is spreading."

The State Department's final environmental analysis of the project is due any day now. Then Obama will have 90 days to decide whether the pipeline is in the U.S. national interest.

A TransCanada official said late Sunday the company has no problem with environmentalists publicly demonstrating against the pipeline.

"We respect the fact that people do have different opinions than we do and we respect their right to say it," Shawn Howard, a company spokesman, said in an interview from Calgary.