diff --git a/src/rules_validation_api/validators/iteration_validator.py b/src/rules_validation_api/validators/iteration_validator.py
index d4934fd25..1c0f713fc 100644
--- a/src/rules_validation_api/validators/iteration_validator.py
+++ b/src/rules_validation_api/validators/iteration_validator.py
@@ -97,6 +97,46 @@ def transform_actions_mapper(cls, action_mapper: ActionsMapper) -> ActionsMapper
         action_mapper.root = new_root
         return action_mapper
 
+    @model_validator(mode="after")
+    def validate_rule_cohort_labels_against_iteration_cohorts(self) -> typing.Self:
+        allowed_labels = {c.cohort_label for c in self.iteration_cohorts}
+        line_errors: list[InitErrorDetails] = []
+
+        # Pre compute allowed label string once
+        allowed_str = ", ".join(sorted(allowed_labels)) if allowed_labels else None
+
+        for idx, rule in enumerate(self.iteration_rules):
+            if not rule.cohort_label:
+                continue
+
+            for label in rule.parsed_cohort_labels:
+                if label in allowed_labels:
+                    continue
+
+                # Build error message
+                error_message = (
+                    f"Invalid cohort_label value '{label}'. Allowed values: {allowed_str}."
+                    if allowed_str
+                    else (
+                        f"Invalid cohort_label value '{label}'. "
+                        "No iteration cohorts are defined, so no labels are allowed."
+                    )
+                )
+
+                line_errors.append(
+                    InitErrorDetails(
+                        type="value_error",
+                        loc=("iteration_rules", idx, "cohort_label"),
+                        input=rule.cohort_label,
+                        ctx={"error": error_message},
+                    )
+                )
+
+        if line_errors:
+            raise ValidationError.from_exception_data(title="IterationValidation", line_errors=line_errors)
+
+        return self
+
     @model_validator(mode="after")
     def action_mapper_validation(self) -> typing.Self:
         all_errors = []
diff --git a/tests/unit/validation/test_campaign_config_validator.py b/tests/unit/validation/test_campaign_config_validator.py
index c0e47e981..7782621b1 100644
--- a/tests/unit/validation/test_campaign_config_validator.py
+++ b/tests/unit/validation/test_campaign_config_validator.py
@@ -13,10 +13,7 @@ class TestMandatoryFieldsSchemaValidations:
     def test_campaign_config_with_only_mandatory_fields_configuration(
         self, valid_campaign_config_with_only_mandatory_fields
     ):
-        try:
-            CampaignConfigValidation(**valid_campaign_config_with_only_mandatory_fields)
-        except ValidationError as e:
-            pytest.fail(f"Unexpected error during model instantiation: {e}")
+        CampaignConfigValidation(**valid_campaign_config_with_only_mandatory_fields)
 
     @pytest.mark.parametrize(
         "mandatory_field",
diff --git a/tests/unit/validation/test_iteration_rules_validator.py b/tests/unit/validation/test_iteration_rules_validator.py
index 1c33f4623..da2e92f43 100644
--- a/tests/unit/validation/test_iteration_rules_validator.py
+++ b/tests/unit/validation/test_iteration_rules_validator.py
@@ -9,10 +9,7 @@ class TestMandatoryFieldsSchemaValidations:
     def test_campaign_config_with_only_mandatory_fields_configuration(
         self, valid_iteration_rule_with_only_mandatory_fields
     ):
-        try:
-            IterationRuleValidation(**valid_iteration_rule_with_only_mandatory_fields)
-        except ValidationError as e:
-            pytest.fail(f"Unexpected error during model instantiation: {e}")
+        IterationRuleValidation(**valid_iteration_rule_with_only_mandatory_fields)
 
     @pytest.mark.parametrize(
         "mandatory_field",
diff --git a/tests/unit/validation/test_iteration_validator.py b/tests/unit/validation/test_iteration_validator.py
index df63cfc11..a9ad48e91 100644
--- a/tests/unit/validation/test_iteration_validator.py
+++ b/tests/unit/validation/test_iteration_validator.py
@@ -14,10 +14,7 @@ class TestMandatoryFieldsSchemaValidations:
     def test_campaign_config_with_only_mandatory_fields_configuration(
         self, valid_campaign_config_with_only_mandatory_fields
     ):
-        try:
-            IterationValidation(**(valid_campaign_config_with_only_mandatory_fields["Iterations"][0]))
-        except ValidationError as e:
-            pytest.fail(f"Unexpected error during model instantiation: {e}")
+        IterationValidation(**(valid_campaign_config_with_only_mandatory_fields["Iterations"][0]))
 
     @pytest.mark.parametrize(
         "mandatory_field",
@@ -556,7 +553,7 @@ def test_iteration_full_datetime_validation(  # noqa : PLR0913
         data = valid_campaign_config_with_only_mandatory_fields.copy()
 
         if default_time_iteration_input:
-            data["iteration_time"] = default_time_iteration_input
+            data["IterationTime"] = default_time_iteration_input
 
         data["Iterations"] = [iteration_data]
 
@@ -570,3 +567,21 @@ def test_iteration_full_datetime_validation(  # noqa : PLR0913
             f"Failed! Input: {iteration_time_input}, Default: {default_time_iteration_input}. "
             f"Expected {expected_date_time} but got {result}"
         )
+
+    def test_iteration_rules_having_invalid_cohort_labels_throws_error(
+        self,
+        valid_iteration_with_only_mandatory_fields,
+        valid_iteration_rule_with_only_mandatory_fields,
+        valid_iteration_cohorts,
+    ):
+        data = valid_iteration_with_only_mandatory_fields.copy()
+        data["IterationRules"] = [valid_iteration_rule_with_only_mandatory_fields]
+        data["IterationCohorts"] = [valid_iteration_cohorts()]
+        data["IterationRules"][0]["CohortLabel"] = "label_2"
+
+        with pytest.raises(ValidationError) as exc_info:
+            IterationValidation(**data)
+
+        errors = exc_info.value.errors()
+        # Ensure at least one error is specifically about the invalid CohortLabel in IterationRules[0]
+        assert any(err.get("loc", [])[:3] == ("iteration_rules", 0, "cohort_label") for err in errors)