Of the 5 proposed pipelines to move tar sands sludge from Canada to refineries or export terminals, 2 have been shut down and 2 have been delayed and forced to start over (including Keystone XL last November). That leave just the Enbridge Line 3 across Minnesota, which because it crosses numerous bodies of water needs approval from the Army Corps of Engineers. For more background you can go here https://www.greenpeace.org/usa/expanding-the-line-3-tar-sands-pipeline-would-put-water-and-climate-at-risk/

The Corps began a 30 day comment period just before the holidays ( of course ) so there is very little time to submit a comment but the folks at Greenpeace have streamlined the process. You can submit a comment through their website https://www.greenpeace.org/usa/