WASHINGTON—President Barack Obama on Tuesday made good on a promise to veto legislation to approve the long-debated Keystone XL pipeline, potentially heralding intensifying clashes between the White House and congressional Republicans.

The bill would have authorized a Canadian company to construct the 1,179-mile pipeline, which has been under review by the Obama administration for more than six years and has become a touchstone issue both for environmentalists and North America’s booming energy industry.

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