Obama sent a two paragraph message to the Senate that read in part:

The Presidential power to veto legislation is one I take seriously. But I also take seriously my responsibility to the American people. And because this act of Congress conflicts with established executive branch procedures and cuts short thorough consideration of issues that could bear on our national interest -- including our security, safety, and environment -- it has earned my veto.

Reuters reports Senate Majority Leader Mitch McConnell says that the Senate will attempt to override the veto by March 3. The Keystone XL pipeline, which has been in political limbo for years, is a planned link between oil fields in Canada and refineries along the Gulf Coast. To read more about the pipeline, take a look at Popular Science's February 2015 analysis of the data behind the politics - the magazine is on sale now in all good newsagencies.