Kerri-Ann Jones of the department said the Republican-backed measure "imposes narrow time constraints and creates automatic mandates," The Hill reported Wednesday.
The bill introduced by GOP Rep. Lee Terry of Nebraska would transfer the pipeline decision from the State Department to the independent Federal Energy Regulatory Commission.
House GOP leaders are considering attaching it to legislation extending the payroll tax holiday to the end of the year.
Jones, the department's point woman on the pipeline project, commented on the legislation in written testimony prepared for delivery to the House Energy and Commerce panel Wednesday.
She defended President Obama's decision last week to reject the pipeline.
The two-month extension of the payroll tax holiday for Americans had called on the president to deal with the pipeline question within 60 days.