President Obama said this week he would weigh the national interest of the Keystone XL against its potential for environmental damage.
"Our national interest will be served only if this project does not significantly exacerbate the problem of carbon pollution," he said in a Tuesday speech at Georgetown University.
Supporters of TransCanada's megapipeline say it will ensure North American energy security while providing a source of economic stimulus. Opponents argue the production of tar sands, the type of crude oil designated for Keystone XL, is more carbon intensive than conventional oil.
Oilchange International, a group opposing the pipeline, said in a statement Wednesday Keystone XL is not a make-or-break project in terms of pollution.
"Stopping Keystone won't magically reverse climate change," the group said. "But for tar sands, like carbon itself, quantity matters. Less is better."
The Canadian government said the science is on the project's side. A U.S. State Department draft review of the project finds there will be environmental consequences tied to tar sands production with or without Keystone XL.
Keystone XL opponent Bold Nebraska said the science is on the side of those opposed to tar sands production. The group wants to build renewable energy projects on the pipeline's planned Nebraska route in protest.