"The president is trying to usurp Congress’s exclusive power of the purse and loot vital funds from our military. Robbing the Defense Department of much-needed funds is an affront to our service members and Congress will strongly oppose any funds for new wall construction," he added.

Pelosi told House Democrats on a caucuswide conference call on Tuesday that Esper also informed her of the move earlier in the day, according to a call participant.

"Canceling military construction projects at home and abroad will undermine our national security and the quality of life and morale of our troops, making America less secure," Pelosi said later in a public statement.

"The House will continue to fight this unacceptable and deeply dangerous decision in the Courts, in the Congress and in the court of public opinion, and honor our oath to protect the Constitution," she added.

Pentagon officials on Tuesday also confirmed that Esper approved $3.6 billion in Defense Department dollars to build 175 miles of wall on the U.S.- Mexico border, with Congress being briefed on the construction projects that will be affected by the order.

The notification to congressional leadership comes following Trump's declaration of a national emergency earlier this year to access more money for the border wall after Congress passed a funding bill that included only $1.35 billion for the border.

Republicans bristled over Trump's decision to declare the national emergency to get wall funding, but Congress was unable to override Trump's veto of a resolution to nix the declaration. Democrats have pledged to force another vote this fall.

As part of the declaration, Trump announced that he would reshuffle $3.6 billion from military construction projects. Republicans are promising to "back fill" the money in the upcoming government funding bills, though that requires cooperation from Democrats.

Cristina Marcos and Ellen Mitchell contributed.