TransCanada Corporation has sued the U.S government over its rejection of the Keystone XL pipeline. On Wednesday, it filed a lawsuit in U.S. federal court alleging President Obama’s rejection of the pipeline exceeded his power under the U.S. Constitution. TransCanada also filed legal action under the North American Free Trade Agreement, or NAFTA, claiming the pipeline permit denial was “arbitrary and unjustified.” It’s seeking $15 billion as part of its NAFTA claim. President Obama rejected the cross-border crude oil pipeline in November, after years of review and one of the most vocal grassroots campaigns this country has seen in decades. We’ll have more on this story after headlines.