The FBI has been making surprise visits to activists protesting the Keystone XL pipeline and the import of oil from Canadian tar sands, stepping up those efforts in recent months, those activists have said.

According to a lawyer who represents some of the activists, the agents have been showing up to houses, calling and texting. They have also shown up to their places of work and contacting family members.

"It's always the same line: 'We're not doing criminal investigations, you're not accused of any crime. But we're trying to learn more about the movement,” the lawyer, Larry Hildes, told YorkRegion.com.

The FBI has responded to the allegations, saying they only investigate possible crimes and that they do not have any interest in peaceful protesters. They may be interested, therefore, in the more than 100,000 people who have signed on to participate in civil disobedience if the Obama Administration approves the go ahead for building the Keystone XL.

However, documents obtained by the Earth Island Journal through a Freedom of Information Act request have revealed collusion between the FBI and TransCanada, the company building the pipeline. As far back as 2012, the agency reached out to the company for “strategy sessions.”

What kind of “strategy” the two organizations may have discussed is unclear but documents obtained in 2013 revealed evidence of TransCanada efforts to get anti-oil activists labeled as “eco-terrorists.”

According to some activists, the FBI has expressed particular interest in the group Deep Green Resistance, one of the founders of which has called for more aggressive tactics.

"I would vastly prefer to wage this struggle non-violently," Lierre Keith told an environmental conference at the University of Oregon. "But my blogging will not bring forth the necessary numbers. So given a realistic assessment of what we actually have, the only viable strategy left that I can see is direct attacks against infrastructure. In the plainest terms, we need to stop them."

However, many of the activists work with organizations that have shown no violent tendencies such as 350.org and Native American groups.