The U.S. military plans to more than double the number of active-duty forces at the southern border, with the new figure disclosed in a letter from a congressional leader admonishing the Pentagon.

More than 3,500 active-duty troops will be sent to the border, according to a letter written by Rep. Adam Smith, D-Wash., chairman of the House Armed Services Committee, in which he slammed Department of Defense officials for not disclosing the figure during a hearing about the border earlier in the week.