Activists stage a sit-in and protest against the Keystone XL pipeline outside the U.S. State Department August 12, 2013 in Washington, DC. Alex Wong/Getty Images

Environmental groups vowed Saturday to challenge the legality of a State Department decision on the controversial Keystone XL pipeline, a day after the project cleared the major political hurdle.

In a report released yesterday, the department said it had no major objections to the 1,179-mile pipeline, which would carry controversial tar sands oil from Canada through the heartland of America to Texas refineries.

Despite the setback to environmental groups and other opponents, those against the project say there is still a strong legal case for denying the federal permit Keystone needs to move forward.

The pipeline now goes to a 30-day comment period and a review by U.S. Secretary of State John Kerry and other agencies.

In the lead up to the final decision, 16 environmental groups -- including the Sierra Club, Friends of the Earth, and the National Resource Defense Council – intend to pursue a possible legal challenge to the State Department decision. Last week, the umbrella movement sent a letter to Kerry outlining their case against the report.

Key to their argument, the groups cite the National Environmental Policy Act (NEPA), a federal law created to ensure that federal agencies consider cumulative environmental impacts when assessing similar projects instead of the impact of each one piecemeal.

“The Department of State is considering at least two Presidential Permit applications for tar sands pipeline projects that are designed to bring tar sands crude oil to U.S. refineries and world markets,” the letter read.

Calgary-based TransCanada Corp.'s Keystone XL pipeline would mean construction of a new pipeline that would transport at least 830,000 barrels per day (bpd). Also Calgary-based Enbridge Inc.’s proposed Alberta Clipper pipeline (Line 67) would increase the capacity of an existing pipeline from 450,000 bpd to 880,000 bpd. The State Department has yet to release its report on the Enbridge project.

“Imagine you have a plot of forest and there are two highways planned that would go through that forest,” Eddie Scher, Senior Communications Specialist for the Sierra Club, told Al Jazeera.

“You can’t do an environmental impact assessment for each one separately – because it’s the entire forest you’re trying to protect.”

Scher says Keystone XL and Enbridge would both exacerbate the national and global problem of carbon pollution, and that it makes no sense to split up the assessment especially when both proposed pipeline expansions are in front of the state concurrently.

President Barack Obama has 90 days to make the final decision on the pipeline, but the White House on Friday disputed the notion that the report is headed for a fast approval.

Project-supporters said the department’s report -- the latest in a five-year review by state and federal agencies – bolsters their case and argue that the pipeline will reduce America’s dependence on overseas oil.

Keystone XL is “not about energy versus the environment. It’s about where Americans want to get their oil,” said Russ Girling, CEO of Calgary-based pipeline developer TransCanada.

Opponents counter that Keystone is an export pipeline and will actually raise gas prices for Americans. Gulf Coast refiners plan to refine the cheap Canadian crude supplied by the pipeline into diesel and other products for export to Europe and Latin America, anti-Keystone group Tar Sands Action said on its website.