diff --git a/facho/fe/form/__init__.py b/facho/fe/form/__init__.py
index 617fba1..2adf261 100644
--- a/facho/fe/form/__init__.py
+++ b/facho/fe/form/__init__.py
@@ -508,7 +508,7 @@ class Invoice:
         self.invoice_prepaid_payment = []
         self.invoice_billing_reference = None
         self.invoice_type_code = str(type_code)
-
+        self.invoice_ident_prefix = None
 
     def set_period(self, startdate, enddate):
         self.invoice_period_start = startdate
@@ -521,7 +521,20 @@ class Invoice:
         self.invoice_issue = dtime
 
     def set_ident(self, ident: str):
+        """
+        identificador de factura; prefijo + consecutivo
+        """
         self.invoice_ident = ident
+        if not self.invoice_ident_prefix:
+            self.invoice_ident_prefix = ident[0:4]
+
+    def set_ident_prefix(self, prefix: str):
+        """
+        prefijo de facturacion: ejemplo SETP
+        """
+        if len(prefix) != 4:
+            raise ValueError('prefix must be 4 length')
+        self.invoice_ident_prefix = prefix
 
     def set_supplier(self, party: Party):
         self.invoice_supplier = party
diff --git a/facho/fe/form_xml/invoice.py b/facho/fe/form_xml/invoice.py
index d9a8caf..40bfe2d 100644
--- a/facho/fe/form_xml/invoice.py
+++ b/facho/fe/form_xml/invoice.py
@@ -174,7 +174,7 @@ class DIANInvoiceXML(fe.FeXML):
         #DIAN 1.7.-2020: FAJ50
         #DIAN 1.7.-2020: CAJ50
         fexml.set_element('./cac:AccountingSupplierParty/cac:Party/cac:PartyLegalEntity/cac:CorporateRegistrationScheme/cbc:ID',
-                          'SETP')
+                          invoice.invoice_ident_prefix)
 
         #DIAN 1.7.-2020: CAJ67
         fexml.placeholder_for('./cac:AccountingSupplierParty/cac:Party/cac:Contact')
diff --git a/tests/test_form.py b/tests/test_form.py
index 006ce31..d3252f0 100644
--- a/tests/test_form.py
+++ b/tests/test_form.py
@@ -174,3 +174,13 @@ def test_invoice_legalmonetary_with_taxes():
     assert inv.invoice_legal_monetary_total.charge_total_amount == form.Amount(0.0)
     assert inv.invoice_legal_monetary_total.payable_amount == form.Amount(100.0)
 
+def test_invoice_ident_prefix_automatic():
+    inv = form.NationalSalesInvoice()
+    inv.set_ident('SETP1234567')
+    assert inv.invoice_ident_prefix == 'SETP'
+
+def test_invoice_ident_prefix_manual():
+    inv = form.NationalSalesInvoice()
+    inv.set_ident('SETP1234567')
+    inv.set_ident_prefix('SETA')
+    assert inv.invoice_ident_prefix == 'SETA'