diff --git a/client/client.go b/client/client.go
index b7b8f874a..44f5a9942 100644
--- a/client/client.go
+++ b/client/client.go
@@ -16,6 +16,14 @@ import (
 	"github.com/twilio/twilio-go/client/form"
 )
 
+var alphanumericRegex *regexp.Regexp
+var delimitingRegex *regexp.Regexp
+
+func init() {
+	alphanumericRegex = regexp.MustCompile(`^[a-zA-Z0-9]*$`)
+	delimitingRegex = regexp.MustCompile(`\.\d+`)
+}
+
 // Credentials store user authentication credentials.
 type Credentials struct {
 	Username string
@@ -87,6 +95,26 @@ func (c *Client) doWithErr(req *http.Request) (*http.Response, error) {
 	return res, nil
 }
 
+// throws error if username and password contains special characters
+func (c *Client) validateCredentials() error {
+	username, password := c.basicAuth()
+	if !alphanumericRegex.MatchString(username) {
+		return &TwilioRestError{
+			Status:   400,
+			Code:     21222,
+			Message:  "Invalid Username. Illegal chars",
+			MoreInfo: "https://www.twilio.com/docs/errors/21222"}
+	}
+	if !alphanumericRegex.MatchString(password) {
+		return &TwilioRestError{
+			Status:   400,
+			Code:     21224,
+			Message:  "Invalid Password. Illegal chars",
+			MoreInfo: "https://www.twilio.com/docs/errors/21224"}
+	}
+	return nil
+}
+
 // SendRequest verifies, constructs, and authorizes an HTTP request.
 func (c *Client) SendRequest(method string, rawURL string, data url.Values,
 	headers map[string]interface{}) (*http.Response, error) {
@@ -101,8 +129,7 @@ func (c *Client) SendRequest(method string, rawURL string, data url.Values,
 	if method == http.MethodGet {
 		if data != nil {
 			v, _ := form.EncodeToStringWith(data, delimiter, escapee, keepZeros)
-			regex := regexp.MustCompile(`\.\d+`)
-			s := regex.ReplaceAllString(v, "")
+			s := delimitingRegex.ReplaceAllString(v, "")
 
 			u.RawQuery = s
 		}
@@ -112,6 +139,11 @@ func (c *Client) SendRequest(method string, rawURL string, data url.Values,
 		valueReader = strings.NewReader(data.Encode())
 	}
 
+	credErr := c.validateCredentials()
+	if credErr != nil {
+		return nil, credErr
+	}
+
 	req, err := http.NewRequest(method, u.String(), valueReader)
 	if err != nil {
 		return nil, err
diff --git a/client/client_test.go b/client/client_test.go
index d1e7d88aa..abf2999c2 100644
--- a/client/client_test.go
+++ b/client/client_test.go
@@ -116,6 +116,28 @@ func TestClient_SendRequestErrorWithDetails(t *testing.T) {
 	assert.Equal(t, details, twilioError.Details)
 }
 
+func TestClient_SendRequestUsernameError(t *testing.T) {
+	newTestClient := NewClient("user1\nuser2", "pass")
+	resp, err := newTestClient.SendRequest("GET", "http://example.org", nil, nil) //nolint:bodyclose
+	twilioError := err.(*twilio.TwilioRestError)
+	assert.Nil(t, resp)
+	assert.Equal(t, 400, twilioError.Status)
+	assert.Equal(t, 21222, twilioError.Code)
+	assert.Equal(t, "https://www.twilio.com/docs/errors/21222", twilioError.MoreInfo)
+	assert.Equal(t, "Invalid Username. Illegal chars", twilioError.Message)
+}
+
+func TestClient_SendRequestPasswordError(t *testing.T) {
+	newTestClient := NewClient("user1", "pass1\npass2")
+	resp, err := newTestClient.SendRequest("GET", "http://example.org", nil, nil) //nolint:bodyclose
+	twilioError := err.(*twilio.TwilioRestError)
+	assert.Nil(t, resp)
+	assert.Equal(t, 400, twilioError.Status)
+	assert.Equal(t, 21224, twilioError.Code)
+	assert.Equal(t, "https://www.twilio.com/docs/errors/21224", twilioError.MoreInfo)
+	assert.Equal(t, "Invalid Password. Illegal chars", twilioError.Message)
+}
+
 func TestClient_SendRequestWithRedirect(t *testing.T) {
 	redirectServer := httptest.NewServer(http.HandlerFunc(
 		func(writer http.ResponseWriter, request *http.Request) {