Washington — The Pentagon on Tuesday formally authorized the transfer of billions of dollars in military funding for the construction of barriers along the U.S.-Mexico border, fulfilling a request by President Trump as he rushes to deliver on his signature campaign promise of building a wall to deter illegal immigration.

Responding to the White House's demand, Secretary of Defense Mark Esper approved the reprogramming of $3.6 billion in military construction funds to be used to build approximately 175 miles of border barriers. Half of the money will be diverted from overseas construction projects by Pentagon, while the other half will be transferred from domestic projects.

About 127 current Department of Defense projects are expected to be affected by the move and the Pentagon is slated to brief lawmakers about the extent of the anticipated delays caused by the transfer, defense officials told CBS News.

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The American Civil Liberties Union said Tuesday the group would be seeking a court order to block the use of the funds.

With a little over a year left until the 2020 presidential election, Mr. Trump has been urging officials to ramp up efforts to build new barriers or replace dilapidated ones in both public and private lands near the southern border as quickly as possible. Along with other promises to crackdown on illegal immigration, Mr. Trump's vow to erect a wall along the border with Mexico proved to be a galvanizing message for his ardent supporters during the 2016 campaign, and he's hoping construction will energize his base for his reelection.

In this April 5, 2019, photo, a U.S. Customs and Border Protection vehicle sits near the a section of the U.S. border wall with Mexico in Calexico, California. AP

After a two-month-long impasse with congressional Democrats that led to the longest government shutdown in U.S. history, Mr. Trump declared a national emergency over immigration in February and vowed to take unilateral action to secure funding for his long-promised border wall. Along with taking funds from other government accounts, the administration said it would tap into billions of funds allocated for the military.

The decision garnered widespread criticism from Democrats and prompted several groups to mount legal challenges against the first $2.5 billion transfer. A federal judge initially blocked this reprogramming but earlier in the summer, the Supreme Court in a 5-4 ruling allowed the administration to use these military funds while litigation over their transfer moves forward.

Democrats in Congress were quick to condemn Tuesday's announcement. Senators Dick Durbin of Illinois, Patrick Leahy of Vermont and Brian Schatz of Hawaii accused the president of politicizing resources for U.S. service members to build his "vanity wall."

"The President is robbing the men and women of our armed services of funds meant for critical construction projects that are necessary to serve our troops, support our allies, deter our adversaries, and care for our military families — all to build a wall that will do nothing to solve the humanitarian crisis at our Southwest border or protect the American people," the senators wrote.

The Trump administration had already pledged to transfer funds from different government accounts not related to immigration for border enforcement.

Last week it was revealed that officials had notified Congress that the Department of Homeland Security is planning to reprogram $271 million funds from several agencies — including the Federal Emergency Management Agency, the Transportation Security Administration and U.S. Coast Guard — to expand space in detention centers for migrants and finance other immigration enforcement initiatives.