"Toys are increasingly ugly and aggressive in form," he said. "Many of them promote negative emotions and the aesthetics of death. In my opinion they have a negative influence on a child's development."
He said some parents need guidance on the effect that toys have on their children.
LEGO spokesman Roar Trangbaek insisted the toys were fun and inspiring, while conflict games have been played for generations.
"You can play out various scenarios and various emotions with the different facial expressions the mini figures have: happy, angry, sad," Trangbaek told the AP. "The beauty of our product is that you can play out whatever you like."
It is not Kostrzewa's first crusade. He has in the past campaigned against Sanrio's Hello Kitty, arguing that it promoted the pornography industry and the sexualizing of young girls.