diff --git a/addons/account_edi_ubl_cii/i18n/account_edi_ubl_cii.pot b/addons/account_edi_ubl_cii/i18n/account_edi_ubl_cii.pot
index 1cd4d6d075b..26724fbed85 100644
--- a/addons/account_edi_ubl_cii/i18n/account_edi_ubl_cii.pot
+++ b/addons/account_edi_ubl_cii/i18n/account_edi_ubl_cii.pot
@@ -837,6 +837,15 @@ msgid ""
 "The field 'Sanitized Account Number' is required on the Recipient Bank."
 msgstr ""
 
+#. module: account_edi_ubl_cii
+#. odoo-python
+#: code:addons/account_edi_ubl_cii/models/account_edi_xml_ubl_bis3.py:0
+#, python-format
+msgid ""
+"The invoice contains line(s) with a negative unit price, which is not "
+"allowed. You might need to set a negative quantity instead."
+msgstr ""
+
 #. module: account_edi_ubl_cii
 #. odoo-python
 #: code:addons/account_edi_ubl_cii/models/account_edi_xml_cii_facturx.py:0
diff --git a/addons/account_edi_ubl_cii/models/account_edi_xml_ubl_bis3.py b/addons/account_edi_ubl_cii/models/account_edi_xml_ubl_bis3.py
index 4bce8d3248a..3ebd7ba6a9f 100644
--- a/addons/account_edi_ubl_cii/models/account_edi_xml_ubl_bis3.py
+++ b/addons/account_edi_ubl_cii/models/account_edi_xml_ubl_bis3.py
@@ -306,6 +306,11 @@ class AccountEdiXmlUBLBIS3(models.AbstractModel):
         }
 
         for line in invoice.invoice_line_ids.filtered(lambda x: x.display_type not in ('line_note', 'line_section')):
+            if invoice.currency_id.compare_amounts(line.price_unit, 0) == -1:
+                # [BR-27]-The Item net price (BT-146) shall NOT be negative.
+                constraints.update({'cen_en16931_positive_item_net_price': _(
+                    "The invoice contains line(s) with a negative unit price, which is not allowed."
+                    " You might need to set a negative quantity instead.")})
             if len(line.tax_ids.flatten_taxes_hierarchy().filtered(lambda t: t.amount_type != 'fixed')) != 1:
                 # [UBL-SR-48]-Invoice lines shall have one and only one classified tax category.
                 # /!\ exception: possible to have any number of ecotaxes (fixed tax) with a regular percentage tax