In the letter, signatories including former secretaries of state Madeleine Albright and John Kerry and former defense secretaries Chuck Hagel and Leon Panetta say they "are aware of no emergency that remotely justifies" the Feb. 15 declaration, Politico reported.
"Under no plausible assessment of the evidence is there a national emergency today that entitles the president to tap into funds appropriated for other purposes to build a wall at the southern border," the letter says, according to The Washington Post. The newspaper was the first to report on the 11-page document.
According to CNN, officials say in the statement that Trump's declaration failed to acknowledge his administration's data on illegal border crossings, which show they are at a nearly 40-year low, and dismiss the president's insistence that terrorism and crime made the declaration imperative.
Officials say in the letter that the declaration "will only exacerbate the humanitarian concerns that do exist at the southern border," according to CNN.
The statement is set to be filed in the Congressional Record one day before lawmakers vote on a House resolution aimed at blocking the emergency declaration, the Post reported.
Members of the House are expected to pass the resolution, forcing the Senate to vote on the measure in the coming weeks, according to Politico. The news site noted that "several of the chamber's Republicans have already expressed unease with the president's decision to circumvent lawmakers."
Trump on Feb. 15 signed the national emergency declaration to funnel over $6 billion in funds from the Treasury Department and the Pentagon to pay to build the border wall, Cox Media Group's Jamie Dupree reported.
The national emergency declaration is already facing several legal challenges, including a lawsuit filed by the attorneys general of 16 states.