"To block the pipeline" means to take action to prevent the progress or development of a project or system, typically by creating obstacles or barriers that impede its functioning. Full definition
In the end environmental reviews and indigenous protests may not be the most effective legal strategy to take in blocking pipeline projects. (macleans.ca)
Today there are a number of actions in solidarity with Indigenous people blocking the pipeline route. (rabble.ca)
That said, reducing emissions by blocking the pipeline would likely be far more costly (primarily in terms of higher world oil prices but also, potentially, in terms of reduced Bakken production) than almost any other emissions - cutting approach that serious people contemplate. (dotearth.blogs.nytimes.com)