Helen Yost, a 62-year-old environmental educator, has been a committed activist for nearly a decade. Yost may not fit the profile of a domestic terrorist, but in 2014 the FBI classified her as a potential threat to national security. According to hundreds of pages of FBI files obtained by the Guardian through a Freedom of Information Act (FOIA) lawsuit, and interviews with activists, Yost and more than a dozen other people campaigning against fossil fuel extraction in North America have been identified in domestic terrorism-related investigations. The investigations, which targeted individual activists and some environmental organizations, were opened in 2013-2014, at the height of opposition to the Keystone XL Pipeline. In 2010, the DoJ's inspector general criticized the FBI for using non-violent civil disobedience as grounds to open domestic terrorism investigations. US citizens swept up in such investigations can be placed on terrorism watchlists and subjected to surveillance and restrictions on international travel. In recent years, Donald Trump has approved construction of the Keystone XL and Dakota Access pipelines, and his administration has also advocated for stiffer penalties against activists who engage in non-violent direct action targeting fossil fuel infrastructure. Meanwhile, in the wake of the Standing Rock protests, seven states have passed legislation making it a crime to trespass on property containing critical infrastructure.