An investigation is looking into U.S. Border Patrol policies on use of lethal force is expected.
The order comes amid a spate of deadly shootings along the border in recent years. Earlier this month a teenager was killed while agents say he was throwing rocks at them from across a fence in Mexico.
Since 2010, at least 18 people have been killed by Border Patrol agents, eight in instances where federal authorities said they were being attacked by rock-throwers. That includes the 2010 incident involving Sergio Adrian Hernandez-Guereca.
Hernandez-Guereca was killed in June of 2010. Earlier this year an agent was dismissed of charges filed against them by Hernandez-Guereca's family.
Vicki Gaubeca, director of the ACLU's Regional Center for Border Rights, in Las Cruces, said deaths along the border are a common occurence.
A probe by the Department of Homeland Security's Office of Inspector General involves a review of accusations of brutality and excessive force as it works to determine whether reforms have been implemented.
The review, briefly referenced in a 100-page report released this month, was launched after 16 members of Congress expressed concern over the 2010 death of an unarmed Mexican migrant in San Diego. They asked the Department of Homeland Security to determine whether the incident is ''emblematic of a broader cultural problem'' within the agency.
''It is ongoing,'' Arlen Morales, a spokeswoman for the Inspector General's Office, said Thursday.
She declined to comment on details of the investigation or when it began, but noted it could take up to a year to complete.
U.S. Customs and Border Protection also would not comment, noting only that it fully cooperates with the Inspector General's Office, agency spokesman Michael Friel said.
The Border Patrol considers the use of deadly force against rock-throwers generally acceptable, noting the projectiles can be deadly, but critics of the practice claim it's an unfair fight.
''It just seems like it's over the top to use lethal force in response to rock throwers,'' Gaubeca said.
Kent Lundgren, a former agent and now chairman of the National Association of Former Border Patrol Officers, countered that rocks can indeed be deadly.
''A rock thrown real slow will kill you just as dead as a bullet,'' Lundgren said, recounting a time in the early 1970s when he was hit in the head while patrolling the border near El Paso, Texas.
"I don't think the policy should be to shoot anyone that picks up a rock," said Lundgren in an interview with ABC-7. "It is self-defense, though. David killed Goliath with a rock, people are still stoned to death in the world we live in today. Rocks are lethal instruments, let's not make any mistake about that."
Mexican officials, meanwhile, have repeatedly decried the use of lethal force in such cases but the denouncements have brought little change among increasing fatalities.
Multiple wrongful death lawsuits have been filed by Mexican families and in at least one case, a Border Patrol agent was charged with murder in Mexico. The agent has not been extradited.
In the most recent case last week, Mexican authorities say a 16-year-old boy was killed by an agent who shot through a border fence in Nogales, Ariz. The Border Patrol acknowledged the agent was responding to rock-throwing but has only said ''it appeared someone had been hit.'' Investigations are ongoing on both sides of the border.
A Mexican official with direct knowledge of the investigation told the AP the boy had been shot multiple times in the back. The person was not yet authorized to discuss details of the case and spoke on condition of anonymity.
Mexico's Foreign Relations Department issued a statement saying it ''forcefully condemned'' the shooting, calling such deaths ''a serious bilateral problem.''