Pipeline advocates — including Republicans, major business groups and some unions — call the project a way to create jobs and boost energy security.
Environmentalists bitterly oppose the project over greenhouse gas emissions and other ecological damage from Alberta’s oil sands projects, as well as fears of spills along the route.
Romney also supports the pipeline, an issue that has shot to the top of Republicans’ agenda on Capitol Hill.
House Republicans plan to attach provisions requiring a pipeline permit to major transportation legislation heading to the floor next week, while Senate GOP leaders are also pushing to overturn Obama’s decision.
Additionally, lawmakers are eyeing inclusion of Keystone provisions in legislation to further extend the payroll tax cut.
Obama last month said he was not rejecting the permit on the merits of the issue, but because Republicans demanded a deadline that would have short-circuited review.
He also invited TransCanada to reapply.