The review follows a call from members of Congress to the IG to look into whether there are "potential legal and constitutional violations" with the deployments, which has been ongoing for more than year.
"Based on several requests, we have decided to conduct an evaluation, in accord with our standard processes, to examine the use of military personnel along the southern border," said Glenn Fine, the acting Inspector General, in a statement obtained by ABC News.
"In this evaluation, we will examine, among other issues, what they are doing at the border, what training they received, and whether their use complied with applicable law, DOD policy, and operating guidance. We intend to conduct this important evaluation as expeditiously as possible," Fine said.
President Donald Trump first deployed National Guard troops to the U.S.-Mexico border in April 2018. Then, in October 2018, more than 5,000 active duty forces were sent to augment support to the Department of Homeland Security.
In a letter to Fine in September, more than 30 members of Congress said they were "strongly concerned" that thousands of U.S. troops were "operating under dubious legal authorities and nebulous rules of engagement." One of those concerns was whether the deployment violated the Posse Comitatus Act which places limits on active duty forces acting in a law enforcement capacity.
The Pentagon has routinely said U.S. troops are supporting Customs and Border Protection, not conducting law enforcement activities.