The Natural Born Killers director was horrified to read reports that the beasts are shot with high-powered rifles and operated on at a course provided in NATO (North Atlantic Treaty Organization) facilities in Jaegerspris, Denmark.
He has now written to Defence Secretary Philip Hammond and urged him to put an end to British participation in the "cruel" drills.
In the email, Stone - who served in the U.S. infantry during the Vietnam War - writes, "Pigs are very intelligent beings - just like the dogs and cats with whom millions of us share our homes.
"Using them as targets and cutting them apart is barbaric and shameful. It is unscrupulous and underhanded for the MoD to outsource this unnecessary cruelty knowing full well that it would not be allowed on British soil.
"The brave men and women who risk their lives to fight for our countries deserve the best possible training, and sending soldiers to participate in reprehensible exercises that inflict severe pain on pigs does not improve the preparedness of the U.K.'s military medical teams.
"Please do not condone cruelty to animals by forcing soldiers to engage in such barbarism."