The veto carries out a threat to reject one of the first measures the Republican-led Congress sent to the president's desk.
The State Department informed eight agencies Friday they have until Feb. 2 to comment on whether the Keystone XL pipeline would serve the national interest.
The White House made formal veto threats Wednesday against House bills that would allow the construction of the Keystone XL pipeline and change a key mandate under the Affordable Care Act.
The senator said whether it gets to Obama's desk could depend on one vote.
The administration won't issue a final Keystone XL pipeline decision until after the midterms, now that a key court case won't be heard until September
Jimmy Carter will urge President Obama Wednesday to block the Keystone XL pipeline
Fifty-six percent of conservative or moderate Democrats back the pipeline, but just 40 percent of liberal Democrats do.
On the final day of public comments on the Keystone pipeline opponents outnumbered supporters 2 to 1.
Warren Buffett and former secretary of state George P. Shultz support the idea.
The State Department IG won't release a report Friday on whether Keystone XL's main contractor had a conflict of interest.