diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7be3c657..d72e06af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -39,6 +39,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 - `tax`: Regime `ChargeKeys` removed. Keys now provided in `bill` package.
 - `it`: Charge keys no longer defined, no migration required, already supported.
 
+### Fixed
+
+- `mx`: Tax ID validation now correctly supports `&` and `Ñ` symbols in codes.
+
 ## [v0.203.0]
 
 ### Added
diff --git a/addons/mx/cfdi/food_vouchers.go b/addons/mx/cfdi/food_vouchers.go
index e64e542a..2beae37c 100644
--- a/addons/mx/cfdi/food_vouchers.go
+++ b/addons/mx/cfdi/food_vouchers.go
@@ -49,6 +49,8 @@ type FoodVouchers struct {
 // one of the customer's employees. It maps to one `Concepto` node in the CFDI's
 // complement.
 type FoodVouchersLine struct {
+	// Line number starting from 1 (calculated).
+	Index int `json:"i" jsonschema:"title=Index" jsonschema_extras:"calculated=true"`
 	// Identifier of the e-wallet that received the food voucher (maps to `Identificador`).
 	EWalletID cbc.Code `json:"e_wallet_id" jsonschema:"title=E-wallet Identifier"`
 	// Date and time of the food voucher's issue (maps to `Fecha`).
@@ -125,7 +127,8 @@ func (fve *FoodVouchersEmployee) Validate() error {
 func (fvc *FoodVouchers) Calculate() error {
 	fvc.Total = num.MakeAmount(0, FoodVouchersFinalPrecision)
 
-	for _, l := range fvc.Lines {
+	for i, l := range fvc.Lines {
+		l.Index = i + 1
 		l.Amount = l.Amount.Rescale(FoodVouchersFinalPrecision)
 
 		fvc.Total = fvc.Total.Add(l.Amount)
diff --git a/addons/mx/cfdi/fuel_account_balance.go b/addons/mx/cfdi/fuel_account_balance.go
index 4972e6fe..921691e6 100644
--- a/addons/mx/cfdi/fuel_account_balance.go
+++ b/addons/mx/cfdi/fuel_account_balance.go
@@ -45,6 +45,8 @@ type FuelAccountBalance struct {
 // issued by the invoice's supplier. It maps to one
 // `ConceptoEstadoDeCuentaCombustible` node in the CFDI's complement.
 type FuelAccountLine struct {
+	// Index of the line starting from 1 (calculated)
+	Index int `json:"i" jsonschema:"title=Index" jsonschema_extras:"calculated=true"`
 	// Identifier of the e-wallet used to make the purchase (maps to `Identificador`).
 	EWalletID cbc.Code `json:"e_wallet_id" jsonschema:"title=E-wallet Identifier"`
 	// Date and time of the purchase (maps to `Fecha`).
@@ -113,6 +115,7 @@ func (fal *FuelAccountLine) Validate() error {
 		validation.Field(&fal.VendorTaxCode,
 			validation.Required,
 			validation.By(mx.ValidateTaxCode),
+			validation.Skip, // don't use default code validations
 		),
 		validation.Field(&fal.ServiceStationCode,
 			validation.Required,
@@ -179,7 +182,8 @@ func (fab *FuelAccountBalance) Calculate() error {
 	taxtotal := num.MakeAmount(0, FuelAccountTotalsPrecision)
 	fab.Subtotal = num.MakeAmount(0, FuelAccountTotalsPrecision)
 
-	for _, l := range fab.Lines {
+	for i, l := range fab.Lines {
+		l.Index = i + 1
 		// Normalise amounts to the expected precision
 		l.Quantity = l.Quantity.RescaleUp(FuelAccountPriceMinimumPrecision)
 		if l.Item != nil {
diff --git a/addons/mx/cfdi/fuel_account_balance_test.go b/addons/mx/cfdi/fuel_account_balance_test.go
index 8aea9049..63bf758f 100644
--- a/addons/mx/cfdi/fuel_account_balance_test.go
+++ b/addons/mx/cfdi/fuel_account_balance_test.go
@@ -23,7 +23,7 @@ func TestInvalidComplement(t *testing.T) {
 	assert.Contains(t, err.Error(), "lines: cannot be blank")
 }
 
-func TestInvalidLine(t *testing.T) {
+func TestFuelAccountInvalidLine(t *testing.T) {
 	fab := &cfdi.FuelAccountBalance{Lines: []*cfdi.FuelAccountLine{{}}}
 
 	err := fab.Validate()
@@ -47,6 +47,10 @@ func TestInvalidLine(t *testing.T) {
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "vendor_tax_code: invalid tax identity code")
 	assert.Contains(t, err.Error(), "total: must be quantity x unit_price")
+
+	fab.Lines[0].VendorTaxCode = "K&A010301I16" // with symbols
+	err = fab.Validate()
+	assert.NotContains(t, err.Error(), "vendor_tax_code")
 }
 
 func TestInvalidItem(t *testing.T) {
@@ -270,6 +274,7 @@ func TestCalculate(t *testing.T) {
 				"total": "12.34",
 				"lines": [
 				  {
+					"i": 1,
 					"e_wallet_id": "",
 					"purchase_date_time": "0000-00-00T00:00:00",
 					"vendor_tax_code": "",
@@ -349,6 +354,7 @@ func TestCalculate(t *testing.T) {
 				"total": "3832.93",
 				"lines": [
 				  {
+					"i": 1,
 					"e_wallet_id": "",
 					"purchase_date_time": "0000-00-00T00:00:00",
 					"vendor_tax_code": "",
diff --git a/data/schemas/regimes/mx/food-vouchers.json b/data/schemas/regimes/mx/food-vouchers.json
index 0f879976..9cedd146 100644
--- a/data/schemas/regimes/mx/food-vouchers.json
+++ b/data/schemas/regimes/mx/food-vouchers.json
@@ -71,6 +71,12 @@
     },
     "FoodVouchersLine": {
       "properties": {
+        "i": {
+          "type": "integer",
+          "title": "Index",
+          "description": "Line number starting from 1 (calculated).",
+          "calculated": true
+        },
         "e_wallet_id": {
           "$ref": "https://gobl.org/draft-0/cbc/code",
           "title": "E-wallet Identifier",
@@ -94,6 +100,7 @@
       },
       "type": "object",
       "required": [
+        "i",
         "e_wallet_id",
         "issue_date_time",
         "amount"
diff --git a/data/schemas/regimes/mx/fuel-account-balance.json b/data/schemas/regimes/mx/fuel-account-balance.json
index 82e9e503..e8c05531 100644
--- a/data/schemas/regimes/mx/fuel-account-balance.json
+++ b/data/schemas/regimes/mx/fuel-account-balance.json
@@ -73,6 +73,12 @@
     },
     "FuelAccountLine": {
       "properties": {
+        "i": {
+          "type": "integer",
+          "title": "Index",
+          "description": "Index of the line starting from 1 (calculated)",
+          "calculated": true
+        },
         "e_wallet_id": {
           "$ref": "https://gobl.org/draft-0/cbc/code",
           "title": "E-wallet Identifier",
@@ -125,6 +131,7 @@
       },
       "type": "object",
       "required": [
+        "i",
         "e_wallet_id",
         "purchase_date_time",
         "vendor_tax_code",
diff --git a/regimes/mx/examples/out/food-vouchers.json b/regimes/mx/examples/out/food-vouchers.json
index 7ddaf99d..4ec30623 100644
--- a/regimes/mx/examples/out/food-vouchers.json
+++ b/regimes/mx/examples/out/food-vouchers.json
@@ -4,7 +4,7 @@
 		"uuid": "8a51fd30-2a27-11ee-be56-0242ac120002",
 		"dig": {
 			"alg": "sha256",
-			"val": "24c15ebc61934602b26715e5a0231761475ef5239084daee7eb2f021acbdc78b"
+			"val": "386eef12c2b78902dfa2ef3b46eb3f06ebcd6909b1d40069417347493f607a54"
 		}
 	},
 	"doc": {
@@ -110,6 +110,7 @@
 				"total": "30.52",
 				"lines": [
 					{
+						"i": 1,
 						"e_wallet_id": "ABC1234",
 						"issue_date_time": "2022-07-19T10:20:30",
 						"employee": {
@@ -121,6 +122,7 @@
 						"amount": "10.12"
 					},
 					{
+						"i": 2,
 						"e_wallet_id": "BCD4321",
 						"issue_date_time": "2022-08-20T11:20:30",
 						"employee": {
diff --git a/regimes/mx/examples/out/fuel-account-balance.json b/regimes/mx/examples/out/fuel-account-balance.json
index 8336c02d..0b6c34f7 100644
--- a/regimes/mx/examples/out/fuel-account-balance.json
+++ b/regimes/mx/examples/out/fuel-account-balance.json
@@ -4,7 +4,7 @@
 		"uuid": "8a51fd30-2a27-11ee-be56-0242ac120002",
 		"dig": {
 			"alg": "sha256",
-			"val": "a0b87156fa951dd596f01301595f2fd83eac97fb4395558ea77df63e4b7d0acd"
+			"val": "274ebf8cbe4ac7864a1f9d9835116f0e86277a06026012e08c8ba566f1833747"
 		}
 	},
 	"doc": {
@@ -110,6 +110,7 @@
 				"total": "400.00",
 				"lines": [
 					{
+						"i": 1,
 						"e_wallet_id": "1234",
 						"purchase_date_time": "2022-07-19T10:20:30",
 						"vendor_tax_code": "RWT860605OF5",
@@ -137,6 +138,7 @@
 						]
 					},
 					{
+						"i": 2,
 						"e_wallet_id": "1234",
 						"purchase_date_time": "2022-08-19T10:20:30",
 						"vendor_tax_code": "DJV320816JT1",
diff --git a/regimes/mx/mx.go b/regimes/mx/mx.go
index f065c5fb..9dec90e0 100644
--- a/regimes/mx/mx.go
+++ b/regimes/mx/mx.go
@@ -58,7 +58,7 @@ func Normalize(doc any) {
 	case *bill.Invoice:
 		normalizeInvoice(obj)
 	case *tax.Identity:
-		tax.NormalizeIdentity(obj)
+		NormalizeTaxIdentity(obj)
 	}
 }
 
diff --git a/regimes/mx/tax_identity.go b/regimes/mx/tax_identity.go
index fe9e794a..e51c53ff 100644
--- a/regimes/mx/tax_identity.go
+++ b/regimes/mx/tax_identity.go
@@ -2,6 +2,7 @@ package mx
 
 import (
 	"regexp"
+	"strings"
 
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/tax"
@@ -30,25 +31,46 @@ const (
 
 // Tax Identity Patterns
 const (
-	TaxIdentityPatternPerson  = `^([A-ZÑ&]{4})([0-9]{6})([A-Z0-9]{3})$`
-	TaxIdentityPatternCompany = `^([A-ZÑ&]{3})([0-9]{6})([A-Z0-9]{3})$`
+	TaxIdentityPatternPerson  = `^([A-ZÑ\&]{4})([0-9]{6})([A-Z0-9]{3})$`
+	TaxIdentityPatternCompany = `^([A-ZÑ\&]{3})([0-9]{6})([A-Z0-9]{3})$`
 )
 
 // Tax Identity Regexp
 var (
 	TaxIdentityRegexpPerson  = regexp.MustCompile(TaxIdentityPatternPerson)
 	TaxIdentityRegexpCompany = regexp.MustCompile(TaxIdentityPatternCompany)
+	TaxCodeBadCharsRegexp    = regexp.MustCompile(`[^A-ZÑ\&0-9]+`)
 )
 
 // ValidateTaxIdentity validates a tax identity for SAT.
 func ValidateTaxIdentity(tID *tax.Identity) error {
+	if tID == nil {
+		return nil
+	}
 	return validation.ValidateStruct(tID,
 		validation.Field(&tID.Code,
 			validation.By(ValidateTaxCode),
+			validation.Skip, // don't apply regular code validation
 		),
 	)
 }
 
+// NormalizeTaxIdentity ensures the tax code is good for mexico
+func NormalizeTaxIdentity(tID *tax.Identity) {
+	if tID == nil {
+		return
+	}
+	tID.Code = NormalizeTaxCode(tID.Code)
+}
+
+// NormalizeTaxCode normalizes a tax code for SAT using the special
+// rules it requires.
+func NormalizeTaxCode(code cbc.Code) cbc.Code {
+	c := strings.ToUpper(code.String())
+	c = TaxCodeBadCharsRegexp.ReplaceAllString(c, "")
+	return cbc.Code(c)
+}
+
 // ValidateTaxCode validates a tax code according to the rules
 // defined by the Mexican SAT.
 func ValidateTaxCode(value interface{}) error {
diff --git a/regimes/mx/tax_identity_test.go b/regimes/mx/tax_identity_test.go
index e43b14ba..592245ec 100644
--- a/regimes/mx/tax_identity_test.go
+++ b/regimes/mx/tax_identity_test.go
@@ -28,6 +28,10 @@ func TestTaxIdentityNormalization(t *testing.T) {
 			Code:     "GHI-701231-23Z",
 			Expected: "GHI70123123Z",
 		},
+		{
+			Code:     "K&A010301I16",
+			Expected: "K&A010301I16",
+		},
 	}
 	for _, ts := range tests {
 		tID := &tax.Identity{Country: "MX", Code: ts.Code}
@@ -36,7 +40,20 @@ func TestTaxIdentityNormalization(t *testing.T) {
 	}
 }
 
+func TestNormalizeTaxIdentity(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		tID := (*tax.Identity)(nil)
+		assert.NotPanics(t, func() {
+			mx.NormalizeTaxIdentity(tID)
+		})
+	})
+}
+
 func TestTaxIdentityValidation(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		tID := (*tax.Identity)(nil)
+		assert.NoError(t, mx.Validate(tID))
+	})
 	tests := []struct {
 		name string
 		code cbc.Code
@@ -47,6 +64,7 @@ func TestTaxIdentityValidation(t *testing.T) {
 		{name: "valid code 1", code: "MNOP8201019HJ"},
 		{name: "valid code 2", code: "UVWX610715JKL"},
 		{name: "valid code 3", code: "STU760612MN1"},
+		{name: "with symbol", code: "K&A010301I16"},
 		{
 			name: "invalid code 1",
 			code: "STU760612MN",
@@ -86,6 +104,13 @@ func TestTaxIdentityValidation(t *testing.T) {
 	}
 }
 
+func TestValidateTaxCode(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		err := mx.ValidateTaxCode("")
+		assert.NoError(t, err)
+	})
+}
+
 func TestTaxIdentityDetermineType(t *testing.T) {
 	tests := []struct {
 		Code cbc.Code