Photos show Australian-born Mary and the royal family of Denmark standing in front of the deer carcasses, smiling and chatting with other members of the crowd.
Several pictures were shared on the Danish royal family’s official Instagram account, @detdanskekongehus, along with a caption: "This morning, the King’s Hunt was held in Gribskov, and this afternoon there was a game parade in front of Fredensborg Castle, where H.M. The Queen, the Crown Prince couple, and the participants of the hunt watched the proceeds of the day."
A number of people took to the comments section to write: "Stop hunting of innocent animals."
Another said: "Mary, you're Australian and should know better. STOP this barbaric hunting of innocent animals. It is an affront to civilised people everywhere!"
"There is nothing noble about shooting defenceless animals for fun," a PETA spokeswoman said.
"Given the now well-established link between cruelty to animals in childhood and violent behaviour in adulthood, not only is it insensitive for Prince Frederik and Princess Mary to teach their children that killing animals is acceptable, it’s also a poor parenting decision," the PETA spokeswoman added.
"Few people today view hunting as anything other than a violent blood sport, a cheap thrill at taking a life and a display of wanton power over the powerless.
"It is surely the parents’ responsibility to help children grow into compassionate leaders for their country, with respect for all living beings."