The National Guard confirmed at least one of the people in the photo is a member who was recently trained to serve on the Funeral Honor Guard unit for veterans' funerals.
The accompanying caption read "We put the FUN in funeral."
Outraged users flooded the guard's Facebook page and posted screenshots of the photo Monday with outraged comments, the Milwaukee Journal Sentinel reported.
Wisconsin Army National Guard Maj. Paul D. Rickert said the outfit was allowing people to post their angry comments on the page without deleting them.
"We're allowing people to vent their frustrations over this very serious matter," he said.
He declined to say whether a formal investigation into the matter has been undertaken.