Leaders from 25 environmental groups sent a letter to President Obama September 24, expressing opposition to any deal between the U.S. and Canada that could result in the approval of the Keystone XL pipeline. Canadian Prime Minister Stephen Harper and other officials had hinted that they were open to a deal to reduce carbon emissions if the U.S. approves the project. Groups represented include Bold Nebraska, the Center for Biological Diversity, Greenpeace, the League of Conservation Voters, Natural Resources Defense Council, and 350.org. The same day, the Sierra Club sent a similar letter to the president.