diff --git a/c/misra/src/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.ql b/c/misra/src/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.ql
new file mode 100644
index 0000000000..5fcf938046
--- /dev/null
+++ b/c/misra/src/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.ql
@@ -0,0 +1,23 @@
+/**
+ * @id c/misra/bit-field-declared-as-member-of-a-union
+ * @name RULE-6-3: A bit field shall not be declared as a member of a union
+ * @description Type punning on a union with bit fields relies on implementation-specific alignment
+ *              behavior.
+ * @kind problem
+ * @precision very-high
+ * @problem.severity warning
+ * @tags external/misra/id/rule-6-3
+ *       correctness
+ *       external/misra/obligation/required
+ */
+
+import cpp
+import codingstandards.c.misra
+
+from BitField field, Union u
+where
+  not isExcluded(field, BitfieldTypes2Package::bitFieldDeclaredAsMemberOfAUnionQuery()) and
+  u.getAField() = field
+select field,
+  "Union member " + field.getName() +
+    " is declared as a bit field which relies on implementation-specific behavior."
diff --git a/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.expected b/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.expected
new file mode 100644
index 0000000000..7c39484796
--- /dev/null
+++ b/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.expected
@@ -0,0 +1,2 @@
+| test.c:7:7:7:7 | x | Union member x is declared as a bit field which relies on implementation-specific behavior. |
+| test.c:20:7:20:7 | (unnamed bitfield) | Union member (unnamed bitfield) is declared as a bit field which relies on implementation-specific behavior. |
diff --git a/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.qlref b/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.qlref
new file mode 100644
index 0000000000..21c43d4826
--- /dev/null
+++ b/c/misra/test/rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.qlref
@@ -0,0 +1 @@
+rules/RULE-6-3/BitFieldDeclaredAsMemberOfAUnion.ql
\ No newline at end of file
diff --git a/c/misra/test/rules/RULE-6-3/test.c b/c/misra/test/rules/RULE-6-3/test.c
new file mode 100644
index 0000000000..1de648d294
--- /dev/null
+++ b/c/misra/test/rules/RULE-6-3/test.c
@@ -0,0 +1,21 @@
+union U1 {
+  int x;  // COMPLIANT
+  char y; // COMPLIANT
+};
+
+union U2 {
+  int x : 2; // NON-COMPLIANT
+  char y;    // COMPLIANT
+};
+
+union U3 {
+  struct str {
+    int x : 4; // COMPLIANT
+    int y : 2; // COMPLIANT
+  };
+};
+
+union U4 {
+  char x;
+  int : 0; // NON-COMPLIANT
+};
\ No newline at end of file
diff --git a/cpp/common/src/codingstandards/cpp/exclusions/c/BitfieldTypes2.qll b/cpp/common/src/codingstandards/cpp/exclusions/c/BitfieldTypes2.qll
new file mode 100644
index 0000000000..ca116bb51c
--- /dev/null
+++ b/cpp/common/src/codingstandards/cpp/exclusions/c/BitfieldTypes2.qll
@@ -0,0 +1,26 @@
+//** THIS FILE IS AUTOGENERATED, DO NOT MODIFY DIRECTLY.  **/
+import cpp
+import RuleMetadata
+import codingstandards.cpp.exclusions.RuleMetadata
+
+newtype BitfieldTypes2Query = TBitFieldDeclaredAsMemberOfAUnionQuery()
+
+predicate isBitfieldTypes2QueryMetadata(Query query, string queryId, string ruleId, string category) {
+  query =
+    // `Query` instance for the `bitFieldDeclaredAsMemberOfAUnion` query
+    BitfieldTypes2Package::bitFieldDeclaredAsMemberOfAUnionQuery() and
+  queryId =
+    // `@id` for the `bitFieldDeclaredAsMemberOfAUnion` query
+    "c/misra/bit-field-declared-as-member-of-a-union" and
+  ruleId = "RULE-6-3" and
+  category = "required"
+}
+
+module BitfieldTypes2Package {
+  Query bitFieldDeclaredAsMemberOfAUnionQuery() {
+    //autogenerate `Query` type
+    result =
+      // `Query` type for `bitFieldDeclaredAsMemberOfAUnion` query
+      TQueryC(TBitfieldTypes2PackageQuery(TBitFieldDeclaredAsMemberOfAUnionQuery()))
+  }
+}
diff --git a/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll b/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
index c2771f4171..2ddc5138b8 100644
--- a/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
+++ b/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
@@ -4,6 +4,7 @@ import codingstandards.cpp.exclusions.RuleMetadata
 //** Import packages for this language **/
 import Banned
 import BitfieldTypes
+import BitfieldTypes2
 import Concurrency1
 import Concurrency2
 import Concurrency3
@@ -75,6 +76,7 @@ import Types1
 newtype TCQuery =
   TBannedPackageQuery(BannedQuery q) or
   TBitfieldTypesPackageQuery(BitfieldTypesQuery q) or
+  TBitfieldTypes2PackageQuery(BitfieldTypes2Query q) or
   TConcurrency1PackageQuery(Concurrency1Query q) or
   TConcurrency2PackageQuery(Concurrency2Query q) or
   TConcurrency3PackageQuery(Concurrency3Query q) or
@@ -146,6 +148,7 @@ newtype TCQuery =
 predicate isQueryMetadata(Query query, string queryId, string ruleId, string category) {
   isBannedQueryMetadata(query, queryId, ruleId, category) or
   isBitfieldTypesQueryMetadata(query, queryId, ruleId, category) or
+  isBitfieldTypes2QueryMetadata(query, queryId, ruleId, category) or
   isConcurrency1QueryMetadata(query, queryId, ruleId, category) or
   isConcurrency2QueryMetadata(query, queryId, ruleId, category) or
   isConcurrency3QueryMetadata(query, queryId, ruleId, category) or
diff --git a/rule_packages/c/BitfieldTypes2.json b/rule_packages/c/BitfieldTypes2.json
new file mode 100644
index 0000000000..d916421b1f
--- /dev/null
+++ b/rule_packages/c/BitfieldTypes2.json
@@ -0,0 +1,21 @@
+{
+  "MISRA-C-2012": {
+    "RULE-6-3": {
+      "properties": {
+        "obligation": "required"
+      },
+      "queries": [
+        {
+          "description": "Type punning on a union with bit fields relies on implementation-specific alignment behavior.",
+          "kind": "problem",
+          "name": "A bit field shall not be declared as a member of a union",
+          "precision": "very-high",
+          "severity": "warning",
+          "short_name": "BitFieldDeclaredAsMemberOfAUnion",
+          "tags": ["correctness"]
+        }
+      ],
+      "title": "A bit field shall not be declared as a member of a union"
+    }
+  }
+}
\ No newline at end of file