diff --git a/src/TransactionBuilder.php b/src/TransactionBuilder.php
index 26e2082..046b10b 100644
--- a/src/TransactionBuilder.php
+++ b/src/TransactionBuilder.php
@@ -518,6 +518,18 @@ public function withExemptLine($amount, $itemCode, $exemptionCode, $lineNumber =
         return $this;
     }
 
+    /**
+     * Add a exemption number for this document
+     *
+     * @param   string              $exemptionNo     Exemption Number for this document.
+     * @return  TransactionBuilder
+     */
+    public function withExemptionNo($exemptionNo)
+    {
+        $this->_model['exemptionNo'] = $exemptionNo;
+        return $this;
+    }
+
     /**
      * Specific a currency code for this transaction
      *