For the first time in five years, President Obama exercised his veto power.
The President rejected legislation that would have given final approval to the Keystone XL oil pipeline.
The planned pipeline would transport oil from Canada to the Gulf of Mexico.
Advocates say the pipeline would create jobs, but opponents say there are too many environmental risks.
The project has been under review by the State Department for years.
A White House Official said yesterday it is possible that the President could approve the pipeline once that review is finished.