Eight days after Nebraska regulators greenlighted the controversial Keystone XL pipeline, Rep. Keith Ellison (D-Minn.) cautioned regulators in his neighboring state against giving swift approval to another proposed oil pipeline.

In a Tuesday letter shared with HuffPost, the progressive congressman urged the Minnesota Public Utilities Commission (MNPUC) to consider climate change, downstream pollution and Native Americans’ fierce opposition before voting on the final certificates needed to begin construction of Enbridge Energy’s Line 3 pipeline. The state regulators are scheduled to hold a Dec. 7 hearing on the project’s potential environmental impact. A final vote is slated for April.

Enbridge’s $2 billion pipeline would carry 760,000 barrels of tar sands oil some 1,031 miles from Alberta, Canada, to refineries in Minnesota every day. That amount of crude is equivalent to the annual carbon emissions of about 16 to 18 million cars on the road, Ellison noted.

“Many of my constituents noted that the Line 3 replacement pipeline would be transporting tar sands crude, which is among the dirtiest fossil fuels,” Ellison wrote. “When reviewing this project, the MNPUC should ensure that the pipeline would not further exacerbate the warming of our planet or undermine Minnesota’s ability to achieve statutory greenhouse gas emission reduction targets.”

Enbridge Energy A map on Enbridge Energy's website shows the proposed route for the Line 3 pipeline.

Tar sands, a noxious mix of clay, sand and oil, are considered one of the most pollutive fossil fuels and could face stricter regulations in Canada in the future. To reduce costs ahead of any crackdown, the industry is looking to scale up the pipelines between the United States and Canada. Enbridge’s Line 3 and TransCanada’s Keystone XL are part of that push.

The Nebraska Public Service Commission voted 3-2 this month to approve the Keystone XL addition, despite the fact that the existing Keystone pipeline had leaked 210,000 gallons of oil in South Dakota just days earlier. It was the biggest spill in the pipeline’s seven-year history, but not the first. The pipeline has had three major accidents since the earlier construction was completed in 2010, far more than TransCanada predicted to regulators, according to Reuters. That has stoked fears that Keystone XL, if completed, could contaminate the Ogallala Aquifer, the largest aquifer in North America.

Ellison cited similar concerns in his letter, noting that Enbridge pipelines had more than 800 spills between 1999 and 2010, according to a Polaris Institute report. That includes a major 2010 spill in the Kalamazoo River in Michigan.

Last month, the Minnesota Public Utilities Commission voted to require Enbridge to publicly disclose its projections for potential spills from the Line 3 pipeline. The company had redacted the data from the public version of its report submitted to the Minnesota Department of Commerce, claiming the information could be used by “bad actors” to damage the pipeline.

Win McNamee via Getty Images Rep. Keith Ellison is considered one of the most progressive voices in Congress.

“Many constituents also expressed concern about the risk posed to downstream communities,” Ellison wrote. “The proposed Line 3 reroute would cross the Red River, the Mississippi, and the Lake Superior watersheds, 192 surface waters, and hundreds of wetland acres. Millions of people and thousands of cities line the shores of the Mississippi, and a spill or leak could have severe consequences on access to drinking water.”

Public opposition to these oil projects has also been driven by the troubles over the Dakota Access Pipeline, a conduit for Bakken crude that cuts through the Standing Rock Sioux’s sacred water. That project prompted huge protests at the reservation, which drew activists, veterans and environmentalists from across the country. Ellison said Enbridge’s proposed route crosses land set aside for the Ojibwe tribe in an 1855 treaty.

“Tribal communities have also shared with me their deep opposition to the pipeline,” Ellison said. “Minnesota must respect our treaties and address the legitimate issues that the pipeline presents to the rights we have guaranteed to our indigenous neighbors.”