The Secret Service has already taken action against 12 of its own employees; Monday's action involved a military member.
Six have been forced out of the Secret Service.
Three Defense Department officials said the 12th military person involved was in Colombia in advance of President Barack Obama's arrival for the Summit of the Americas and was assigned to the White House Communications Agency, a military unit that provides secure communications for the president. The defense officials, who spoke on the condition of anonymity because the investigation is ongoing, said he is an enlisted man. One of the officials said he is in the Army.
Another of the officials said the soldier has been relieved of his duties at the White House.
The Associated Press contributed to this report.