diff --git a/CHANGES.rst b/CHANGES.rst
index 0e56957067..3069853c64 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -40,6 +40,8 @@ associations
   for S1600A1 with 5 point dithers, to reduce overlap between background nods
   and science exposure. [#8744]
   
+- Added association rule for level 3 image mosaic candidates. [#8798]
+
 badpix_selfcal
 --------------
 
diff --git a/jwst/associations/lib/rules_level3.py b/jwst/associations/lib/rules_level3.py
index ac64e1128e..bd1b4d1f54 100644
--- a/jwst/associations/lib/rules_level3.py
+++ b/jwst/associations/lib/rules_level3.py
@@ -25,6 +25,7 @@
     'Asn_Lv3ACQ_Reprocess',
     'Asn_Lv3AMI',
     'Asn_Lv3Image',
+    'Asn_Lv3ImageMosaic',
     'Asn_Lv3ImageBackground',
     'Asn_Lv3MIRCoron',
     'Asn_Lv3MIRMRS',
@@ -466,7 +467,7 @@ def __init__(self, *args, **kwargs):
                         value = ('T')
                     )],
                     reduce=Constraint.notany
-                ),  
+                ),
                 DMSAttrConstraint(
                     name='channel',
                     sources=['channel'],
@@ -1172,3 +1173,72 @@ def __init__(self, *args, **kwargs):
     @property
     def dms_product_name(self):
         return dms_product_name_sources(self)
+
+
+@RegistryMarker.rule
+class Asn_Lv3ImageMosaic(AsnMixin_Science):
+    """Level 3 Science Image Mosaic Association
+
+    Characteristics:
+        - Association type: ``image3``
+        - Pipeline: ``calwebb_image3``
+        - Non-TSO
+        - Non-WFS&C
+        - Collect separate tiles of mosaic into one product
+    """
+
+    def __init__(self, *args, **kwargs):
+
+        # Setup constraints
+        self.constraints = Constraint([
+            Constraint_Optical_Path(),
+            Constraint_Image(),
+            DMSAttrConstraint(
+                name='wfsvisit',
+                sources=['visitype'],
+                value='((?!wfsc).)*',
+                required=False
+            ),
+            Constraint(
+                [
+                    DMSAttrConstraint(
+                        name='bkgdtarg',
+                        sources=['bkgdtarg'],
+                    ),
+                    Constraint_TSO()
+                ],
+                reduce=Constraint.notany
+            ),
+        ])
+
+        # Only valid if candidate type is 'mosaic'.
+        self.validity.update({
+            'is_type_mosaic': {
+                'validated': False,
+                'check': self._validate_candidates
+            }
+        })
+
+        # Now check and continue initialization.
+        super(Asn_Lv3ImageMosaic, self).__init__(*args, **kwargs)
+
+    def _init_hook(self, item):
+        """Post-check and pre-add initialization"""
+
+        self.data['asn_type'] = 'image3'
+        super(Asn_Lv3ImageMosaic, self)._init_hook(item)
+
+    def _validate_candidates(self, item):
+        """Allow only mosaic asn candidates
+
+        Returns
+        -------
+        True if candidate type is mosaic.
+        False otherwise.
+        """
+
+        # If a group candidate, reject.
+        if self.acid.type.lower() != 'mosaic':
+            return False
+
+        return True
diff --git a/jwst/regtest/test_associations_sdp_pools.py b/jwst/regtest/test_associations_sdp_pools.py
index 3c63554fda..3cbe4afe08 100644
--- a/jwst/regtest/test_associations_sdp_pools.py
+++ b/jwst/regtest/test_associations_sdp_pools.py
@@ -147,6 +147,12 @@
         'xfail': None,
         'slow': False,
     },
+    # This association tests the Asn_Lv3ImageMosaic rule
+    'jw02739_20230710t150016_pool': {
+        'args': ['-i', 'c1000'],
+        'xfail': None,
+        'slow': False,
+    },
     'jw80600_20171108T041522_pool': {
         'args': [],
         'xfail': 'PR #3450',