Critics of an oil pipeline extension say U.S. President Barack Obama's job depends on blocking the proposed Keystone XL pipeline. The Washington Post reported that U.S. State Department is expected to release its final environmental assessment of TransCanada's planned Keystone XL pipeline as early as Friday. The project is an extension to an existing pipeline carrying oil from tar sands in Alberta, Canada. Opponents say the record of heavy Alberta crude suggests Keystone XL isn't worth the risk. A group of environmental activists ranging from Greenpeace to the Rainforest Action Network, in a letter to Obama, said his political career depends on block this "terrible project." "If you block it, you will trigger a surge of enthusiasm from the green base that supported you so strongly in the last election," the letter states. Opponents protested the project in front of the White House during the weekend, leading to dozens of arrests. The Post reports that the State Department's assessment will back early sentiments that Keystone XL will have "limited adverse environmental impacts." TransCanada said the project would include technology that would make it one of the safest pipelines in the United States.