Sen. Mary Landrieu on Thursday said she will block the nomination of Jacob Lew to serve as director of the Office of Management and Budget until the Obama administration promises to lift a moratorium on deep-water oil drilling.

In a letter sent Thursday to Majority Leader Harry Reid (D-Nev.), the Louisiana Democrat said, “I cannot in good conscience allow this nomination to proceed until I receive a commitment from Mr. Lew, the President or another senior economic advisor to reverse these policies.

“I do not take this step lightly,” she added. But Landrieu described her decision as a last resort after months of protesting President Barack Obama’s six-month drilling moratorium, which was implemented in response to the BP Deepwater Horizon spill in April that poured millions of gallons of oil into the Gulf of Mexico.

“I have done everything within my power to get this administration’s attention,” she said. “But the policy remains in effect, and Louisiana’s economy continues to suffer.”

Lew’s nomination has been widely hailed in the Senate, and Democratic leaders had hoped the chamber would approve his confirmation before adjourning for the pre-election recess. But Reid would have to file time-consuming procedural motions to overcome Landrieu’s roadblock, which he is unlikely to do in the waning days before the fall break.

Lew, who is the deputy secretary of State for management and resources and served as OMB director under President Bill Clinton from 1998 to 2001, was approved 22-1 by the Budget Committee on Thursday. The Homeland Security and Governmental Affairs panel, which shares jurisdiction over the nomination, unanimously approved him during a Tuesday markup. Landrieu is a member of that panel, although she did not vote on the nomination.