Excommunicate

is_available = trigger_if = {
	limit = {
		is_ai = yes
	}
	piety >= major_piety_value
	is_adult = yes
}
is_shown = scope:puppet_or_actor ?= {
	this != scope:recipient
	is_clergy = yes
	is_ruler = yes
	faith ?= {
		this = scope:recipient.faith
		faith_has_sacraments_central_trigger = yes
		trigger_if = {
			limit = {
				religious_head ?= scope:puppet_or_actor
			}
			has_doctrine = doctrine_spiritual_head
		}
		NOT = {
			religious_head ?= scope:recipient
		}
	}
}

As written in game/common/character_interactions/00_religious_interactions.txt.

NOR = {
	scope:recipient = {
		has_character_modifier = excommunication_recently_lifted
	}
	scope:puppet_or_actor.faith.great_holy_war ?= {
		has_pledged_attacker = scope:recipient
	}
}
scope:puppet_or_actor = {
	highest_held_title_tier >= tier_duchy
	piety >= excommunication_piety_cost_value
	custom_tooltip = {
		text = HOF_INTERACTION_UNREFORMED_FAITH
		NOT = {
			faith = {
				has_doctrine_parameter = unreformed
			}
		}
	}
	NOT = {
		has_trait = excommunicated
	}
}
scope:recipient = {
	NOT = {
		has_strong_hook = scope:puppet_or_actor
	}
}
custom_tooltip = {
	text = cannot_take_overt_hostile_actions_against_diarch.tt
	NOT = {
		scope:recipient ?= scope:puppet_or_actor.diarch
	}
}
scope:recipient = {
	custom_tooltip = {
		text = cannot_excommunicate_antipope_protected_tt
		NOT = {
			pam_antipope_protected_from_excommunication_trigger = {
				EXCOMMUNICATOR = scope:puppet_or_actor
			}
		}
	}
	NOT = {
		has_trait = excommunicated
	}
	pam_valid_excommunication_target_trigger = {
		EXCOMMUNICATOR = scope:puppet_or_actor
	}
}

As written in game/common/character_interactions/00_religious_interactions.txt.

on_accept = if = {
	limit = {
		scope:is_puppet_action ?= yes
	}
	scope:puppet_or_actor = {
		add_piety = {
			value = {
				value = excommunication_piety_cost_value
				max = piety
				multiply = -1
			}
		}
	}
}
scope:puppet_or_actor = {
	if = {
		limit = {
			any_character_situation = {
				situation_type = the_christian_church
			}
			situation:the_christian_church ?= {
				situation_top_has_catalyst = catalyst_excommunicate
			}
		}
		if = {
			limit = {
				scope:recipient = {
					highest_held_title_tier >= tier_kingdom
				}
			}
			situation:the_christian_church = {
				trigger_situation_catalyst = catalyst_excommunicate
			}
		}
		else = {
			situation:the_christian_church = {
				trigger_situation_catalyst = catalyst_excommunicate_minor
			}
		}
	}
}
excommunicate_character = {
	EXCOMMUNICATOR = scope:puppet_or_actor
	REQUESTING_CHARACTER = scope:puppet_or_actor
	TARGET_CHARACTER = scope:recipient
}
scope:recipient = {
	trigger_event = {
		id = religious_interaction.1021
		days = 5
	}
}
add_clan_unity_interaction_effect = {
	CHARACTER = scope:puppet_or_actor
	TARGET = scope:recipient
	VALUE = medium_unity_loss
	DESC = clan_unity_excommunication.desc
	REVERSE_NON_HOUSE_TARGET = no
}

As written in game/common/character_interactions/00_religious_interactions.txt.