diff --git a/l10n_it_vat_settlement_date/models/account_move.py b/l10n_it_vat_settlement_date/models/account_move.py
index e4bbcfb01b0d..c1f067c8fc05 100644
--- a/l10n_it_vat_settlement_date/models/account_move.py
+++ b/l10n_it_vat_settlement_date/models/account_move.py
@@ -2,7 +2,8 @@
 # Copyright 2024 Simone Rubino - Aion Tech
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
-from odoo import api, fields, models
+from odoo import _, api, fields, models
+from odoo.tools import format_date
 
 
 class AccountMove(models.Model):
@@ -25,3 +26,49 @@ def _compute_l10n_it_vat_settlement_date(self):
                 move.date or move.invoice_date or fields.Date.context_today(move)
             )
             move.l10n_it_vat_settlement_date = settlement_date
+
+    def _get_violated_lock_dates(self, invoice_date, has_tax):
+        settlement_date = self.l10n_it_vat_settlement_date
+        if has_tax and settlement_date and invoice_date == self.date:
+            # When tax is involved,
+            # VAT Settlement Date is the date that has to be after the lock.
+            invoice_date = settlement_date
+        return super()._get_violated_lock_dates(invoice_date, has_tax)
+
+    def _get_lock_date_message(self, invoice_date, has_tax):
+        message = super()._get_lock_date_message(invoice_date, has_tax)
+        if message:
+            lock_dates = self._get_violated_lock_dates(invoice_date, has_tax)
+            settlement_date = self.l10n_it_vat_settlement_date
+            if lock_dates and has_tax and settlement_date and invoice_date == self.date:
+                # The super's message talks about a generic date.
+                # When tax is involved,
+                # VAT Settlement Date is the date that has to be after the lock,
+                # and it will be moved too.
+                lock_date, lock_type = lock_dates[-1]
+                unlocked_invoice_date = self._get_accounting_date(invoice_date, has_tax)
+                message = _(
+                    "The VAT Settlement Date is being set "
+                    "prior to the %(lock_type)s lock date %(lock_date)s.\n"
+                    "The Journal Entry will be accounted "
+                    "on %(unlocked_invoice_date)s upon posting.",
+                    lock_type=lock_type,
+                    lock_date=format_date(self.env, lock_date),
+                    unlocked_invoice_date=format_date(self.env, unlocked_invoice_date),
+                )
+            message = "\n".join(
+                [
+                    message,
+                    _(
+                        "Both VAT Settlement Date and accounting date "
+                        "will be changed upon posting.",
+                    ),
+                ]
+            )
+        return message
+
+    @api.depends(
+        "l10n_it_vat_settlement_date",
+    )
+    def _compute_tax_lock_date_message(self):
+        return super()._compute_tax_lock_date_message()
diff --git a/l10n_it_vat_settlement_date/tests/__init__.py b/l10n_it_vat_settlement_date/tests/__init__.py
index 2d4ef90063e5..84b8d6d340bb 100644
--- a/l10n_it_vat_settlement_date/tests/__init__.py
+++ b/l10n_it_vat_settlement_date/tests/__init__.py
@@ -1,4 +1,5 @@
 #  License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
 
+from . import test_lock_dates
 from . import test_vat_period_end_statement
 from . import test_vat_registry
diff --git a/l10n_it_vat_settlement_date/tests/test_lock_dates.py b/l10n_it_vat_settlement_date/tests/test_lock_dates.py
new file mode 100644
index 000000000000..548e50f8a493
--- /dev/null
+++ b/l10n_it_vat_settlement_date/tests/test_lock_dates.py
@@ -0,0 +1,64 @@
+#  Copyright 2024 Simone Rubino - Aion Tech
+#  License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+import datetime
+
+from odoo.tests import tagged
+
+from odoo.addons.account.tests.common import AccountTestInvoicingCommon
+
+
+@tagged("post_install", "-at_install")
+class TestLockDates(AccountTestInvoicingCommon):
+    @classmethod
+    def setUpClass(cls, chart_template_ref=None):
+        super().setUpClass(chart_template_ref=chart_template_ref)
+        cls.company = cls.env.company
+
+    def test_bill_tax_lock(self):
+        """The tax lock date is checked against
+        the settlement date of a supplier bill."""
+        settlement_date = datetime.date(2020, month=1, day=1)
+        tax_lock_date = datetime.date(2020, month=1, day=2)
+        accounting_date = datetime.date(2020, month=1, day=3)
+        self.company.tax_lock_date = tax_lock_date
+        bill = self.init_invoice(
+            "in_invoice",
+            invoice_date=accounting_date,
+            amounts=[100],
+        )
+        # pre-condition
+        self.assertEqual(bill.date, accounting_date)
+        self.assertEqual(bill.invoice_date, accounting_date)
+        self.assertTrue(settlement_date < tax_lock_date < accounting_date)
+        self.assertFalse(bill.tax_lock_date_message)
+
+        # Act
+        bill.l10n_it_vat_settlement_date = settlement_date
+
+        # Assert
+        self.assertIn("VAT Settlement Date", bill.tax_lock_date_message)
+
+    def test_invoice_tax_lock(self):
+        """The tax lock date is checked against
+        the settlement date of a customer invoice."""
+        settlement_date = datetime.date(2020, month=1, day=1)
+        tax_lock_date = datetime.date(2020, month=1, day=2)
+        accounting_date = datetime.date(2020, month=1, day=3)
+        self.company.tax_lock_date = tax_lock_date
+        invoice = self.init_invoice(
+            "out_invoice",
+            invoice_date=accounting_date,
+            amounts=[100],
+        )
+        # pre-condition
+        self.assertEqual(invoice.date, accounting_date)
+        self.assertEqual(invoice.invoice_date, accounting_date)
+        self.assertTrue(settlement_date < tax_lock_date < accounting_date)
+        self.assertFalse(invoice.tax_lock_date_message)
+
+        # Act
+        invoice.l10n_it_vat_settlement_date = settlement_date
+
+        # Assert
+        self.assertIn("VAT Settlement Date", invoice.tax_lock_date_message)