The phrase "to reject the pipeline" means to say no to building or approving a new pipeline. It implies refusing to allow the construction or expansion of a pipeline infrastructure. Full definition
And that is why President Obama rejected the pipeline in 2015. (nrdc.org)
President Barack Obama's administration rejected the pipeline in 2015. (bloomberg.com)
IHS CERA's new environmental assessment of the Keystone XL pipeline and pipeline - related oil sands development sends a pretty clear message to President Obama as he decides whether to approve the full project's construction: There's not a climate rationale for rejecting the pipeline — and along with it, tens of thousands of U.S. jobs, economic uplift and greater energy security. (energytomorrow.org)