Turkeys are a social bird. Pecking is a way for them to demonstrate dominance over not only other turkeys, but other animals and even humans. Both male and female turkeys have their own unique "pecking order," in which the dominant member pecks at the more submissive one. Dominance issues can be hard to eliminate, but there are ways to remove the turkey from the situation where it wants to peck.
Demonstrate dominance. All turkeys must see humans as superior in the "pecking order." Don't hurt the turkey, but physically respond to pecking by pushing the bird aside, or pushing it away with a broom, to demonstrate to the turkey you are not submissive.
Separate the nuisance turkey. If the turkey is pecking at other fowl or animals you have, place them in a different spaces. If they continue to peck when you return them to their original pen, consider a permanent separate enclosure.
Move shiny objects away from turkeys. Even turkeys adjusted to life alongside humans peck at shiny objects such as mirrors, windows and other material. The website MassWildlife recommends keeping a tied-up dog nearby the object you want to protect. That way your property won't be damaged, and the turkey will learn to avoid the area.
Get the turkeys when they're young. Growing up, the turkeys will be more familiar with the "pecking order" that has you on top. According to MassWildlife, home-grown turkeys will recognize and respond to you by both voice and appearance. Wild turkeys will repeatedly challenge humans if they see the people as lower on the "pecking order."