Spc. Terry Harrison, a member of the Madison, Wis.-based 1st Battalion, 147th Aviation Regiment, posted the photo of 14 National Guard members posing in front of an empty, flag-draped casket during training at a base in Arkansas, NBC News reported Wednesday.
The caption on the Instagram photo read "We put the FUN in funerals -- your fearless honor guard from various states."
Wisconsin National Guard Maj. Paul Rickerts said officials do not know who the other people in the photo are but the Guard is investigating the matter.
Harrison has been suspended from performing funeral duties for deceased veterans and Rickerts said the National Guard has taken steps to protect the woman because she has received death threats, Stars and Stripes reported.
An unidentified military official told NBC though the casket, which many people assumed was holding a service member's body, was empty, the group's conduct is still unacceptable.
"These are essentially kids blowing off a little steam, but given the serious and solemn nature of their mission, [funeral duty], their actions are inappropriate and totally unacceptable," the defense official told NBC News.
In addition to the casket photo, Harrison posted a selfie to her Instagram account complaining about having to attend a funeral in winter weather.
"It's so damn cold out. Why have a funeral outside!? Somebody's getting a jacked up flag," the photo's caption reads.