Washington — Active-duty members of the military deployed near the U.S.-Mexico border have been assigned to spend a month painting a mile-long stretch of barriers to improve their "aesthetic appearance."

Lawmakers were notified of the action on Wednesday in an email message from the Department of Homeland Security (DHS), which has asked the Pentagon multiple times in recent months to deploy troops near the southern border to support the agency as it faces an unprecedented surge of Central American families and unaccompanied children heading to or in between ports of entry.

According to the email, the text of which was provided to CBS News by a congressional aide, an unspecified number of service members were set to paint barriers in the California border town of Calexico. The task, according to the email, would last approximately 30 days.

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"While the primary purpose is to improve the aesthetic appearance of the wall, there may also be an operational benefit based on our experience with painted barrier in Nogales, Arizona," the email read.

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

A Customs and Border Protection (CBP) official confirmed the assignment to CBS News, indicating the Department of Defense was asked to conduct the "application" of the paint, with CBP financing the paint and "associated materials." The estimated cost of the paint and equipment is approximately $150,000, the official added.

U.S. Northern Command also confirmed the painting of border barriers, saying the Pentagon is providing around 100 active-duty personnel to apply "anti-climb coating" to part of a new bollard wall near the Calexico West port of entry. Northern Command did not make any reference to improving the "aesthetic appearance" of the border barriers — which CBP said is the primary objective of the operation.

In its notification to Congress, DHS said painting of border barriers near Tucson, Arizona, had allowed Border Patrol to combat the "camouflaging tactics of illegal border crossers" who sought to evade detection. The agency said migrants also appeared to have "greater difficulty" scaling painted bollards along the border.

Some barriers along the southwestern border, including in Nogales, have been painted white, a color which border officials say makes it easier for them to detect migrants compared to the typical brown color. Last month, however, The Washington Post reported that President Trump was pressing officials to paint the barriers black so that they would absorb heat and become too hot for migrants to climb. CBP has not specified what color the Calexico border fences will be painted.

On Twitter, Illinois Sen. Dick Durbin, the second-highest Democrat in the Senate, denounced the task as a "disgraceful misuse" of taxpayer money. "Our military has more important work to do than making Trump's wall beautiful," he added.

DHS informed Congress today that troops are going to spend the next month painting the border wall & “the primary purpose is to improve the aesthetic appearance.” A disgraceful misuse of taxpayer $$. Our military has more important work to do than making Trump’s wall beautiful. — Senator Dick Durbin (@SenatorDurbin) June 5, 2019

Texas Rep. Joaquin Castro, chair of the Congressional Hispanic Caucus, echoed Durbin's comments, calling the task detailed in the email a "gross misuse" of the military.

"These are soldiers, they are not painters," Castro told CBS News.

So far, the military has approved nine requests for assistance from DHS. The painting assignment in Calexico was part of DHS's seventh request — which, according to a Newsweek report, was approved by the Pentagon in April.