WASHINGTON (CNN) -- Leading Senate and House Republicans urged House Speaker Nancy Pelosi, D-California, Monday to call the chamber back into session "immediately," in order to move a House and Senate-backed Iraq spending bill to the president "as quickly as possible."

Both the Senate and the House have passed versions of a spending bill that include a withdrawal deadline. Differences between the two measures have to be ironed out by both chambers before the bill can be sent to President Bush. Bush has vowed to veto any bill that includes a withdrawal deadline.

"We are writing to urge you to call the House back into session immediately so that Congress can finish its work on the emergency legislation to fund the Global War on Terrorism," the congressmen wrote in a letter to Pelosi dated Monday. "This funding request has been pending since February 5, but your leadership team chose to leave town for more than two weeks rather than completing this bill. As a result, our troops have been put at risk."

Democratic leaders have accused Republicans of overstating the risk of delaying final passage of the measure, pointing to a non-partisan Congressional Research Service report that says the Pentagon does not need the funding until July.

Brendan Daly, communications director for Pelosi, called the GOP request a "cheap political stunt," and said House and Senate Democrats have been working on the measure during the congressional break.

The House is currently scheduled to reconvene on April 16.

Senate Minority Leader Mitch McConnell, R-Kentucky, and House Minority Leader John Boehner, R-Ohio, were among those who signed the letter.

-- CNN's Alexander Mooney and Deirdre Walsh