diff --git a/app/models/validations/property_validations.rb b/app/models/validations/property_validations.rb
index e11632544..d520b6dae 100644
--- a/app/models/validations/property_validations.rb
+++ b/app/models/validations/property_validations.rb
@@ -13,4 +13,10 @@ module Validations::PropertyValidations
       record.errors.add :la, "Local authority has to be in London"
     end
   end
+
+  def validate_unitletas(record)
+    if record.unitletas.present? && (record.rsnvac == "First let of newbuild property" || record.rsnvac == "First let of conversion/rehabilitation/acquired property" || record.rsnvac == "First let of leased property")
+      record.errors.add :unitletas, "Can not be completed if it is the first let of the property"
+    end
+  end
 end
diff --git a/spec/features/form/validations_spec.rb b/spec/features/form/validations_spec.rb
index 4aa72e261..4a78c4cf5 100644
--- a/spec/features/form/validations_spec.rb
+++ b/spec/features/form/validations_spec.rb
@@ -162,4 +162,19 @@ RSpec.describe "validations" do
       end
     end
   end
+
+  describe "Property Validations" do
+    context "first let of property and reason for vacancy completed" do
+      let(:rsnvac) { "First let of newbuild property" }
+      let(:rsnvac1) { "First let of conversion/rehabilitation/acquired property" }
+      let(:rsnvac2) { "First let of leased property" }
+      let(:unitletas) { "Social rent basis" }
+
+      it "throws a validation error", js: true do
+        expect { case_log.update!(rsnvac: rsnvac, unitletas: unitletas) }.to raise_error(ActiveRecord::RecordInvalid)
+        expect { case_log.update!(rsnvac: rsnvac1, unitletas: unitletas) }.to raise_error(ActiveRecord::RecordInvalid)
+        expect { case_log.update!(rsnvac: rsnvac2, unitletas: unitletas) }.to raise_error(ActiveRecord::RecordInvalid)
+      end
+    end
+  end
 end