diff --git a/ghmap/cli.py b/ghmap/cli.py
index eaf25c0..d834e82 100644
--- a/ghmap/cli.py
+++ b/ghmap/cli.py
@@ -189,6 +189,16 @@ def _parse_args() -> argparse.Namespace:
         default=None,
         help='Path to a custom action to activity mapping JSON file.'
     )
+    parser.add_argument(
+        '--mapping-strategy',
+        choices=['strict', 'flexible'],
+        default='flexible',
+        help=(
+            "Mapping strategy to handle unknown actions. "
+            "'strict' raises an error on UnknownAction, "
+            "'flexible' issues a warning once and continues (default: flexible)."
+        )
+    )
     return parser.parse_args()
 
 
@@ -228,7 +238,7 @@ def _apply_custom_mappings(
     if args.custom_action_mapping:
         action_mapping = load_json_file(args.custom_action_mapping)
         action_mapper = ActionMapper(action_mapping, progress_bar=args.progress_bar)
-        all_actions = action_mapper.map(events)
+        all_actions = action_mapper.map(events, args.mapping_strategy)
 
     if args.custom_activity_mapping:
         activity_mapping = load_json_file(args.custom_activity_mapping)
@@ -269,7 +279,7 @@ def _process_period(
     # Step 1: Event to Action Mapping
     action_mapping = load_json_file(valid_mappings['action'])
     action_mapper = ActionMapper(action_mapping, progress_bar=args.progress_bar)
-    actions = action_mapper.map(period_events)
+    actions = action_mapper.map(period_events, args.mapping_strategy)
 
     # Step 2: Action to Activity Mapping
     activity_mapping = load_json_file(valid_mappings['activity'])
diff --git a/ghmap/mapping/action_mapper.py b/ghmap/mapping/action_mapper.py
index 6a15479..4b1f339 100644
--- a/ghmap/mapping/action_mapper.py
+++ b/ghmap/mapping/action_mapper.py
@@ -136,11 +136,20 @@ def _extract_field(event_record: Dict, field_path: str) -> Any:
                 return None
         return value
 
-    def map(self, events: List[Dict]) -> List[Dict]:
-        """Maps events to high-level actions using mapping configuration."""
+    def map(self, events: List[Dict], mapping_strategy: str = "flexible") -> List[Dict]:
+        """
+        Maps events to high-level actions using mapping configuration.
+
+        mapping_strategy: "strict" or "flexible"
+        - strict: raise an error on UnknownAction
+        - flexible: tolerate UnknownAction and issue a warning once
+        """
         all_mapped_actions = []
+        unknown_warning_issued = False  # only warn once in flexible mode
 
-        for event_record in tqdm(events, desc="Mapping events to actions", unit="event", disable=not self.progress_bar): # pylint: disable=line-too-long
+        for event_record in tqdm(
+            events, desc="Mapping events to actions", unit="event", disable=not self.progress_bar
+        ):
             if 'payload' in event_record:
                 event_record = self._deserialize_payload(event_record)
             event_record = self._convert_date_to_iso(event_record)
@@ -162,11 +171,23 @@ def map(self, events: List[Dict]) -> List[Dict]:
                     all_mapped_actions.append(mapped_action)
                     break
             else:
-                mapped_action = self._extract_attributes(
-                    event_record,
-                    self.action_mapping['actions']['UnknownAction'],
-                    'UnknownAction'
-                )
-                all_mapped_actions.append(mapped_action)
+                # Handle UnknownAction based on strategy
+                if mapping_strategy == "strict":
+                    raise ValueError(
+                        f"UnknownAction encountered for event: {event_record}"
+                    )
+                if mapping_strategy == "flexible":
+                    if not unknown_warning_issued:
+                        print("Warning: Some actions not identified and mapped as UnknownAction.")
+                        unknown_warning_issued = True
+
+                    mapped_action = self._extract_attributes(
+                        event_record,
+                        self.action_mapping['actions']['UnknownAction'],
+                        'UnknownAction'
+                    )
+                    all_mapped_actions.append(mapped_action)
+                else:
+                    raise ValueError(f"Invalid mapping_strategy: {mapping_strategy}")
 
         return all_mapped_actions