diff --git a/addons/br/nfse/extensions.go b/addons/br/nfse/extensions.go
index 86d7c8b2..607a6f99 100644
--- a/addons/br/nfse/extensions.go
+++ b/addons/br/nfse/extensions.go
@@ -14,6 +14,7 @@ import (
 const (
 	ExtKeyCNAE            = "br-nfse-cnae"
 	ExtKeyFiscalIncentive = "br-nfse-fiscal-incentive"
+	ExtKeyISSLiability    = "br-nfse-iss-liability"
 	ExtKeyMunicipality    = "br-nfse-municipality"
 	ExtKeyService         = "br-nfse-service"
 	ExtKeySimplesNacional = "br-nfse-simples-nacional"
@@ -70,6 +71,74 @@ var extensions = []*cbc.KeyDefinition{
 			`),
 		},
 	},
+	{
+		Key: ExtKeyISSLiability,
+		Name: i18n.String{
+			i18n.EN: "ISS Liability",
+			i18n.PT: "Exigibilidade ISS",
+		},
+		Values: []*cbc.ValueDefinition{
+			{
+				Value: "1",
+				Name: i18n.String{
+					i18n.EN: "Liable",
+					i18n.PT: "Exigível",
+				},
+			},
+			{
+				Value: "2",
+				Name: i18n.String{
+					i18n.EN: "Not subject",
+					i18n.PT: "Não incidência",
+				},
+			},
+			{
+				Value: "3",
+				Name: i18n.String{
+					i18n.EN: "Exempt",
+					i18n.PT: "Isenção",
+				},
+			},
+			{
+				Value: "4",
+				Name: i18n.String{
+					i18n.EN: "Export",
+					i18n.PT: "Exportação",
+				},
+			},
+			{
+				Value: "5",
+				Name: i18n.String{
+					i18n.EN: "Immune",
+					i18n.PT: "Imunidade",
+				},
+			},
+			{
+				Value: "6",
+				Name: i18n.String{
+					i18n.EN: "Suspended Judicially",
+					i18n.PT: "Suspensa por Decisão Judicial",
+				},
+			},
+			{
+				Value: "7",
+				Name: i18n.String{
+					i18n.EN: "Suspended Administratively",
+					i18n.PT: "Suspensa por Processo Administrativo",
+				},
+			},
+		},
+		Desc: i18n.String{
+			i18n.EN: here.Doc(`
+				Indicates the ISS liability status, i.e., whether the ISS tax is due or not and why.
+
+				List of codes taken from the national NFSe standard:
+
+				* https://abrasf.org.br/biblioteca/arquivos-publicos/nfs-e-manual-de-orientacao-do-contribuinte-2-04/download
+				(Section 10.2, Field B-38)
+			`),
+		},
+	},
 	{
 		Key: ExtKeyMunicipality,
 		Name: i18n.String{
diff --git a/addons/br/nfse/nfse.go b/addons/br/nfse/nfse.go
index 4497e0bc..fe4c1727 100644
--- a/addons/br/nfse/nfse.go
+++ b/addons/br/nfse/nfse.go
@@ -40,6 +40,8 @@ func validate(doc any) error {
 		return validateLine(obj)
 	case *org.Item:
 		return validateItem(obj)
+	case *tax.Combo:
+		return validateTaxCombo(obj)
 	}
 	return nil
 }
@@ -48,5 +50,7 @@ func normalize(doc any) {
 	switch obj := doc.(type) {
 	case *bill.Invoice:
 		normalizeSupplier(obj.Supplier)
+	case *tax.Combo:
+		normalizeTaxCombo(obj)
 	}
 }
diff --git a/addons/br/nfse/tax_combo.go b/addons/br/nfse/tax_combo.go
new file mode 100644
index 00000000..2879c08d
--- /dev/null
+++ b/addons/br/nfse/tax_combo.go
@@ -0,0 +1,35 @@
+package nfse
+
+import (
+	"github.com/invopop/gobl/regimes/br"
+	"github.com/invopop/gobl/tax"
+	"github.com/invopop/validation"
+)
+
+const (
+	// ISSLiabilityDefault is the default value for the ISS liability extension
+	ISSLiabilityDefault = "1" // Liable
+)
+
+func validateTaxCombo(tc *tax.Combo) error {
+	return validation.ValidateStruct(tc,
+		validation.Field(&tc.Ext,
+			validation.When(tc.Category == br.TaxCategoryISS,
+				tax.ExtensionsRequires(ExtKeyISSLiability),
+			),
+		),
+	)
+}
+
+func normalizeTaxCombo(tc *tax.Combo) {
+	if tc == nil || tc.Category != br.TaxCategoryISS {
+		return
+	}
+
+	if !tc.Ext.Has(ExtKeyISSLiability) {
+		if tc.Ext == nil {
+			tc.Ext = make(tax.Extensions)
+		}
+		tc.Ext[ExtKeyISSLiability] = ISSLiabilityDefault
+	}
+}
diff --git a/addons/br/nfse/tax_combo_test.go b/addons/br/nfse/tax_combo_test.go
new file mode 100644
index 00000000..86e6b982
--- /dev/null
+++ b/addons/br/nfse/tax_combo_test.go
@@ -0,0 +1,105 @@
+package nfse_test
+
+import (
+	"testing"
+
+	"github.com/invopop/gobl/addons/br/nfse"
+	"github.com/invopop/gobl/regimes/br"
+	"github.com/invopop/gobl/tax"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTaxComboValidation(t *testing.T) {
+	addon := tax.AddonForKey(nfse.V1)
+
+	tests := []struct {
+		name string
+		tc   *tax.Combo
+		err  string
+	}{
+		{
+			name: "valid ISS tax combo",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryISS,
+				Ext: tax.Extensions{
+					nfse.ExtKeyISSLiability: "1",
+				},
+			},
+		},
+		{
+			name: "valid non-ISS tax combo",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryPIS,
+			},
+		},
+		{
+			name: "missing ISS liability",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryISS,
+			},
+			err: "br-nfse-iss-liability: required",
+		},
+	}
+	for _, ts := range tests {
+		t.Run(ts.name, func(t *testing.T) {
+			err := addon.Validator(ts.tc)
+			if ts.err == "" {
+				assert.NoError(t, err)
+			} else {
+				if assert.Error(t, err) {
+					assert.ErrorContains(t, err, ts.err)
+				}
+			}
+		})
+	}
+}
+
+func TestTaxComboNormalization(t *testing.T) {
+	addon := tax.AddonForKey(nfse.V1)
+
+	tests := []struct {
+		name string
+		tc   *tax.Combo
+		out  tax.ExtValue
+	}{
+		{
+			name: "no tax combo",
+			tc:   nil,
+		},
+		{
+			name: "sets default ISS liability",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryISS,
+			},
+			out: "1",
+		},
+		{
+			name: "does not override ISS liability",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryISS,
+				Ext: tax.Extensions{
+					nfse.ExtKeyISSLiability: "2",
+				},
+			},
+			out: "2",
+		},
+		{
+			name: "non-ISS tax combo",
+			tc: &tax.Combo{
+				Category: br.TaxCategoryPIS,
+			},
+		},
+	}
+	for _, ts := range tests {
+		t.Run(ts.name, func(t *testing.T) {
+			addon.Normalizer(ts.tc)
+			if ts.tc == nil {
+				assert.Nil(t, ts.tc)
+			} else {
+				assert.NotNil(t, ts.tc)
+				assert.Equal(t, ts.out, ts.tc.Ext[nfse.ExtKeyISSLiability])
+			}
+		})
+	}
+
+}
diff --git a/data/addons/br-nfse-v1.json b/data/addons/br-nfse-v1.json
index 1230978e..7dca06f4 100644
--- a/data/addons/br-nfse-v1.json
+++ b/data/addons/br-nfse-v1.json
@@ -41,6 +41,67 @@
         }
       ]
     },
+    {
+      "key": "br-nfse-iss-liability",
+      "name": {
+        "en": "ISS Liability",
+        "pt": "Exigibilidade ISS"
+      },
+      "desc": {
+        "en": "Indicates the ISS liability status, i.e., whether the ISS tax is due or not and why.\n\nList of codes taken from the national NFSe standard:\n\n* https://abrasf.org.br/biblioteca/arquivos-publicos/nfs-e-manual-de-orientacao-do-contribuinte-2-04/download\n(Section 10.2, Field B-38)"
+      },
+      "values": [
+        {
+          "value": "1",
+          "name": {
+            "en": "Liable",
+            "pt": "Exigível"
+          }
+        },
+        {
+          "value": "2",
+          "name": {
+            "en": "Not subject",
+            "pt": "Não incidência"
+          }
+        },
+        {
+          "value": "3",
+          "name": {
+            "en": "Exempt",
+            "pt": "Isenção"
+          }
+        },
+        {
+          "value": "4",
+          "name": {
+            "en": "Export",
+            "pt": "Exportação"
+          }
+        },
+        {
+          "value": "5",
+          "name": {
+            "en": "Immune",
+            "pt": "Imunidade"
+          }
+        },
+        {
+          "value": "6",
+          "name": {
+            "en": "Suspended Judicially",
+            "pt": "Suspensa por Decisão Judicial"
+          }
+        },
+        {
+          "value": "7",
+          "name": {
+            "en": "Suspended Administratively",
+            "pt": "Suspensa por Processo Administrativo"
+          }
+        }
+      ]
+    },
     {
       "key": "br-nfse-municipality",
       "name": {
diff --git a/examples/br/invoice-services.json b/examples/br/invoice-services.json
index 1c7be41f..9c985ff7 100644
--- a/examples/br/invoice-services.json
+++ b/examples/br/invoice-services.json
@@ -79,7 +79,10 @@
       "taxes": [
         {
           "cat": "ISS",
-          "percent": "15%"
+          "percent": "15%",
+          "ext": {
+            "br-nfse-iss-liability": "1"
+          }
         }
       ]
     }
diff --git a/examples/br/out/invoice-services.json b/examples/br/out/invoice-services.json
index 90fc13be..d93efb63 100644
--- a/examples/br/out/invoice-services.json
+++ b/examples/br/out/invoice-services.json
@@ -4,7 +4,7 @@
 		"uuid": "8a51fd30-2a27-11ee-be56-0242ac120002",
 		"dig": {
 			"alg": "sha256",
-			"val": "31573fb261adbfa6011c8c21e5e53c4a7546389e6a39fc47124d0e34fb698811"
+			"val": "6b9933fc6209359b95583878eb64c358ac1b9028727c3e992ec4e78f7a196687"
 		}
 	},
 	"doc": {
@@ -91,7 +91,10 @@
 				"taxes": [
 					{
 						"cat": "ISS",
-						"percent": "15%"
+						"percent": "15%",
+						"ext": {
+							"br-nfse-iss-liability": "1"
+						}
 					}
 				],
 				"total": "1500.00"
@@ -106,6 +109,9 @@
 						"code": "ISS",
 						"rates": [
 							{
+								"ext": {
+									"br-nfse-iss-liability": "1"
+								},
 								"base": "1500.00",
 								"percent": "15%",
 								"amount": "225.00"
diff --git a/regimes/br/README.md b/regimes/br/README.md
index 6530e6ea..57a38e53 100644
--- a/regimes/br/README.md
+++ b/regimes/br/README.md
@@ -181,4 +181,31 @@ For example:
 //...
 ```
 
+#### ISS Liability
 
+Report the ISS liability -i.e. whether the tax is due or not and why– using the `br-nfse-iss-liability` extension at ISS tax level. Find the list of possible codes below:
+
+| Code | Description                |
+| ---- | -------------------------- |
+| `1`  | Liable (Default)           |
+| `2`  | Not subject                |
+| `3`  | Exempt                     |
+| `4`  | Export                     |
+| `5`  | Immune                     |
+| `6`  | Suspended Judicially       |
+| `7`  | Suspended Administratively |
+
+For example:
+
+```js
+"lines": [
+  {
+//...
+    "taxes": [
+      {
+        "cat": "ISS",
+        "ext": {
+          "br-nfse-iss-liability": "1"
+        }
+//...
+```