diff --git a/httpx/models.py b/httpx/models.py
index df5d071..32e412f 100644
--- a/httpx/models.py
+++ b/httpx/models.py
@@ -89,16 +89,10 @@ class URL:
         params: QueryParamTypes = None,
     ) -> None:
         if isinstance(url, str):
-            self._uri_reference = rfc3986.api.uri_reference(url)
+            self._uri_reference = rfc3986.api.iri_reference(url).encode()
         else:
             self._uri_reference = url._uri_reference
 
-        # Handle IDNA domain names.
-        if self._uri_reference.authority:
-            idna_authority = self._uri_reference.authority.encode("idna").decode("ascii")
-            if idna_authority != self._uri_reference.authority:
-                self._uri_reference = self._uri_reference.copy_with(authority=idna_authority)
-
         # Normalize scheme and domain name.
         if self.is_absolute_url:
             self._uri_reference = self._uri_reference.normalize()

diff --git a/tests/models/test_url.py b/tests/models/test_url.py
index 7c865f5..a556ed8 100644
--- a/tests/models/test_url.py
+++ b/tests/models/test_url.py
@@ -1,13 +1,65 @@
 import pytest
+import rfc3986
 
 from httpx import URL
 from httpx.exceptions import InvalidURL
 
 
-def test_idna_url():
-    url = URL("http://中国.icom.museum:80/")
-    assert url == URL("http://xn--fiqs8s.icom.museum:80/")
-    assert url.host == "xn--fiqs8s.icom.museum"
+@pytest.mark.parametrize(
+    "given,idna,host,scheme,port",
+    [
+        (
+            "http://中国.icom.museum:80/",
+            "http://xn--fiqs8s.icom.museum:80/",
+            "xn--fiqs8s.icom.museum",
+            "http",
+            80,
+        ),
+        (
+            "http://Königsgäßchen.de",
+            "http://xn--knigsgchen-b4a3dun.de",
+            "xn--knigsgchen-b4a3dun.de",
+            "http",
+            80,
+        ),
+        ("https://faß.de", "https://xn--fa-hia.de", "xn--fa-hia.de", "https", 443),
+        (
+            "https://βόλος.com:443",
+            "https://xn--nxasmm1c.com:443",
+            "xn--nxasmm1c.com",
+            "https",
+            443,
+        ),
+        (
+            "http://ශ්‍රී.com:444",
+            "http://xn--10cl1a0b660p.com:444",
+            "xn--10cl1a0b660p.com",
+            "http",
+            444,
+        ),
+        (
+            "https://نامه‌ای.com:4433",
+            "https://xn--mgba3gch31f060k.com:4433",
+            "xn--mgba3gch31f060k.com",
+            "https",
+            4433,
+        ),
+    ],
+    ids=[
+        "http_with_port",
+        "unicode_tr46_compat",
+        "https_without_port",
+        "https_with_port",
+        "http_with_custom_port",
+        "https_with_custom_port",
+    ],
+)
+def test_idna_url(given, idna, host, scheme, port):
+    url = URL(given)
+    assert url == URL(idna)
+    assert url.host == host
+    assert url.scheme == scheme
+    assert url.port == port
 
 
 def test_url():

Use IDNA 2008 instead of IDNA 2003
Using `str.encode("idna")` uses IDNA 2003 which isn't recommended for modern use. We should be using IDNA 2008 provided by the `idna` module (which is a dependency of `httpx` but I don't think we're using it anywhere?)
tests/models/test_url.py::test_idna_url[unicode_tr46_compat] tests/models/test_url.py::test_idna_url[https_without_port] tests/models/test_url.py::test_idna_url[https_with_port] tests/models/test_url.py::test_idna_url[http_with_custom_port] tests/models/test_url.py::test_idna_url[https_with_custom_port]
tests/models/test_url.py::test_idna_url[http_with_port] tests/models/test_url.py::test_url tests/models/test_url.py::test_url_eq_str tests/models/test_url.py::test_url_params tests/models/test_url.py::test_url_join tests/models/test_url.py::test_url_join_rfc3986 tests/models/test_url.py::test_url_set tests/models/test_url.py::test_hsts_preload_converted_to_https