The Obama administration announced Friday that it is extending the comment period on the State Department's Keystone XL pipeline report -- a move that could delay a final decision on the project indefinitely.
The State Department's report found that the pipeline would not have a significant environmental impact. It was due to be finalized after a 90-day comment period ended in early May.
The debate over TransCanada's $5.3 billion proposed pipeline from northern Alberta to the Gulf Coast has long been a sore point between the Obama administration, environmentalists and lawmakers. The pipeline would carry tar sands oil across six U.S. states.
Environmentalists decry the project because they say the process of extracting and refining tar sands contributes more heavily to climate change than conventional oil production.
"This is a huge victory for climate champions and communities from Alberta down to Nebraska and the Gulf," said Rachel Wolf, a spokesperson for All Risk, No Reward Coalition, a group opposing the pipeline. "Every day without Keystone XL is a day that we keep high-carbon tar sands in the ground."
The pipeline's supporters, such as Senate Minority Leader Mitch McConnell, say research since 2008, when the project was first proposed, has shown the pipeline wouldn't significantly increase greenhouse gas emissions.
"It is crystal clear that the Obama administration is simply not serious about American energy and American jobs," McConnell said in a statement Friday.
McConnell added that he is disappointed the president hasn't done more on the matter by way of executive action.
"I guess he wasn't serious about having a pen and a phone, either," McConnell said in the statement.
Pipeline supporter Rep. Lee Terry, R-Nebraska, also blasted the delay.
"Today, (President Obama) punted a tough decision in the name of political expediency," Terry said in a statement sent to CNN.
"It's shameful that as we begin spring construction season, that hundreds of my constituents will be denied an opportunity to go to work on a project that will help secure America's energy future solely because the President wants to placate his political base in an election year."
Obama, who in his State of the Union speech underscored climate change as a priority of his administration, has said the pipeline must be basically carbon-neutral, meaning it must have little to no effect on climate change.
A Pew Research Center poll conducted in late February through mid-March found that 61% of Americans back the project, compared to 27% who oppose it.
Republicans such as McConnell argue the pipeline is critical to help shore up the economy. Labor unions are hoping the pipeline project can boost jobs.
And four politically-embattled Democrats - Mary Landrieu in Louisiana, Mark Begich in Alaska, Mark Pryor in Arkansas and Kay Hagan of North Carolina -- also want the pipeline.
"This decision is irresponsible, unnecessary and unacceptable," said Landrieu, chairwoman of the Senate Energy Committee in a press statement Friday. "I plan to use my power as chair of the Senate Energy Committee to take decisive action to get this pipeline approved."
CNN's Greg Botelho contributed to this report.
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