If you have a parenting plan in place, you will expect that the other parent will respect this. However, if they intentionally or consistently violate the parenting plan, you should take this very seriously. There are possibilities for you to take action to enforce this.
You should first take the time to review the details of the parenting plan and ensure that the other parent has indeed violated the order. When you have done this, you may want to engage in written communication to notify the other parent of the violation. You may want to do this before getting the law involved because the other parent may not have realized the seriousness of their actions and may agree not to violate the plan again.