diff --git a/tracer/src/Datadog.Trace/SpanExtensions.cs b/tracer/src/Datadog.Trace/SpanExtensions.cs
index e447752cf567..a09ff31e9b46 100644
--- a/tracer/src/Datadog.Trace/SpanExtensions.cs
+++ b/tracer/src/Datadog.Trace/SpanExtensions.cs
@@ -3,6 +3,10 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
 // </copyright>
 
+using System;
+using System.Text;
+using Datadog.Trace.Logging;
+using Datadog.Trace.Tagging;
 using Datadog.Trace.Util;
 
 namespace Datadog.Trace
@@ -12,6 +16,8 @@ namespace Datadog.Trace
     /// </summary>
     public static class SpanExtensions
     {
+        private static readonly IDatadogLogger Log = DatadogLogging.GetLoggerFor(typeof(SpanExtensions));
+
         /// <summary>
         /// Sets the details of the user on the local root span
         /// </summary>
@@ -29,37 +35,51 @@ public static void SetUser(this ISpan span, UserDetails userDetails)
                 ThrowHelper.ThrowArgumentException(nameof(userDetails) + ".Id must be set to a value other than null or the empty string", nameof(userDetails));
             }
 
-            var localRootSpan = span;
+            TraceContext traceContext = null;
             if (span is Span spanClass)
             {
-                localRootSpan = spanClass.Context.TraceContext?.RootSpan ?? span;
+                traceContext = spanClass.Context.TraceContext;
             }
 
-            localRootSpan.SetTag(Tags.User.Id, userDetails.Id);
+            Action<string, string> setTag =
+                traceContext != null
+                    ? (name, value) => traceContext.Tags.SetTag(name, value)
+                    : (name, value) => span.SetTag(name, value);
+
+            if (userDetails.PropagateId)
+            {
+                var base64UserId = Convert.ToBase64String(Encoding.UTF8.GetBytes(userDetails.Id));
+                const string propagatedUserIdTag = TagPropagation.PropagatedTagPrefix + Tags.User.Id;
+                setTag(propagatedUserIdTag, base64UserId);
+            }
+            else
+            {
+                setTag(Tags.User.Id, userDetails.Id);
+            }
 
             if (userDetails.Email is not null)
             {
-                localRootSpan.SetTag(Tags.User.Email, userDetails.Email);
+                setTag(Tags.User.Email, userDetails.Email);
             }
 
             if (userDetails.Name is not null)
             {
-                localRootSpan.SetTag(Tags.User.Name, userDetails.Name);
+                setTag(Tags.User.Name, userDetails.Name);
             }
 
             if (userDetails.SessionId is not null)
             {
-                localRootSpan.SetTag(Tags.User.SessionId, userDetails.SessionId);
+                setTag(Tags.User.SessionId, userDetails.SessionId);
             }
 
             if (userDetails.Role is not null)
             {
-                localRootSpan.SetTag(Tags.User.Role, userDetails.Role);
+                setTag(Tags.User.Role, userDetails.Role);
             }
 
             if (userDetails.Scope is not null)
             {
-                localRootSpan.SetTag(Tags.User.Scope, userDetails.Scope);
+                setTag(Tags.User.Scope, userDetails.Scope);
             }
         }
     }
diff --git a/tracer/src/Datadog.Trace/UserDetails.cs b/tracer/src/Datadog.Trace/UserDetails.cs
index bbb117f4e7a7..e7c3d9803682 100644
--- a/tracer/src/Datadog.Trace/UserDetails.cs
+++ b/tracer/src/Datadog.Trace/UserDetails.cs
@@ -16,7 +16,7 @@ public struct UserDetails
         /// <summary>
         /// Initializes a new instance of the <see cref="UserDetails"/> struct.
         /// </summary>
-        /// <param name="id">The unique identifier assoicated with the users</param>
+        /// <param name="id">The unique identifier associated with the users</param>
         public UserDetails(string id)
         {
             if (string.IsNullOrEmpty(id))
@@ -25,6 +25,7 @@ public UserDetails(string id)
             }
 
             Id = id;
+            PropagateId = false;
             Email = null;
             Name = null;
             SessionId = null;
@@ -43,10 +44,20 @@ public UserDetails(string id)
         public string? Name { get; set; }
 
         /// <summary>
-        /// Gets or sets the unique identifier assoicated with the users
+        /// Gets or sets the unique identifier associated with the user.
         /// </summary>
         public string Id { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether the Id field should be propagated to other services called.
+        /// NOTE: setting this value to true will automatically propagate the Id field to all downstream services
+        /// including any third-party services called by the application. Therefore this value should only be set
+        /// to true if the user is confident that it is safe to propagate the value to all downstream services
+        /// called by the application.
+        /// Default value is false.
+        /// </summary>
+        public bool PropagateId { get; set; }
+
         /// <summary>
         /// Gets or sets the user's session unique identifier
         /// </summary>
diff --git a/tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.PublicApiHasNotChanged.verified.txt b/tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.PublicApiHasNotChanged.verified.txt
index b5bb01f09017..913e81c38bba 100644
--- a/tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.PublicApiHasNotChanged.verified.txt
+++ b/tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.PublicApiHasNotChanged.verified.txt
@@ -348,6 +348,7 @@ namespace Datadog.Trace
         public string? Email { get; set; }
         public string Id { get; set; }
         public string? Name { get; set; }
+        public bool PropagateId { get; set; }
         public string? Role { get; set; }
         public string? Scope { get; set; }
         public string? SessionId { get; set; }
diff --git a/tracer/test/Datadog.Trace.Tests/TracerTests.cs b/tracer/test/Datadog.Trace.Tests/TracerTests.cs
index c34636b8f680..0fbc1175e5a8 100644
--- a/tracer/test/Datadog.Trace.Tests/TracerTests.cs
+++ b/tracer/test/Datadog.Trace.Tests/TracerTests.cs
@@ -528,7 +528,7 @@ public async Task ForceFlush()
         }
 
         [Fact]
-        public void SetUserOnRootSpanDirectly()
+        public void SetUserOnRootSpanDirectly_ShouldSetOnTrace()
         {
             var scopeManager = new AsyncLocalScopeManager();
 
@@ -538,8 +538,8 @@ public void SetUserOnRootSpanDirectly()
             };
             var tracer = new Tracer(settings, Mock.Of<IAgentWriter>(), Mock.Of<ISampler>(), scopeManager, Mock.Of<IDogStatsd>());
 
-            var rootTestScope = tracer.StartActive("test.trace");
-            var childTestScope = tracer.StartActive("test.trace.child");
+            var rootTestScope = (Scope)tracer.StartActive("test.trace");
+            var childTestScope = (Scope)tracer.StartActive("test.trace.child");
             childTestScope.Dispose();
 
             var email = "test@adventure-works.com";
@@ -560,16 +560,17 @@ public void SetUserOnRootSpanDirectly()
             };
             tracer.ActiveScope?.Span.SetUser(userDetails);
 
-            Assert.Equal(email, rootTestScope.Span.GetTag(Tags.User.Email));
-            Assert.Equal(name, rootTestScope.Span.GetTag(Tags.User.Name));
-            Assert.Equal(id, rootTestScope.Span.GetTag(Tags.User.Id));
-            Assert.Equal(sessionId, rootTestScope.Span.GetTag(Tags.User.SessionId));
-            Assert.Equal(role, rootTestScope.Span.GetTag(Tags.User.Role));
-            Assert.Equal(scope, rootTestScope.Span.GetTag(Tags.User.Scope));
+            var traceContext = rootTestScope.Span.Context.TraceContext;
+            Assert.Equal(email, traceContext.Tags.GetTag(Tags.User.Email));
+            Assert.Equal(name, traceContext.Tags.GetTag(Tags.User.Name));
+            Assert.Equal(id, traceContext.Tags.GetTag(Tags.User.Id));
+            Assert.Equal(sessionId, traceContext.Tags.GetTag(Tags.User.SessionId));
+            Assert.Equal(role, traceContext.Tags.GetTag(Tags.User.Role));
+            Assert.Equal(scope, traceContext.Tags.GetTag(Tags.User.Scope));
         }
 
         [Fact]
-        public void SetUserOnChildChildSpan_ShouldAttachToRoot()
+        public void SetUserOnChildChildSpan_ShouldSetOnTrace()
         {
             var scopeManager = new AsyncLocalScopeManager();
 
@@ -579,8 +580,8 @@ public void SetUserOnChildChildSpan_ShouldAttachToRoot()
             };
             var tracer = new Tracer(settings, Mock.Of<IAgentWriter>(), Mock.Of<ISampler>(), scopeManager, Mock.Of<IDogStatsd>());
 
-            var rootTestScope = tracer.StartActive("test.trace");
-            var childTestScope = tracer.StartActive("test.trace.child");
+            var rootTestScope = (Scope)tracer.StartActive("test.trace");
+            var childTestScope = (Scope)tracer.StartActive("test.trace.child");
 
             var email = "test@adventure-works.com";
             var name = "Jane Doh";
@@ -602,12 +603,13 @@ public void SetUserOnChildChildSpan_ShouldAttachToRoot()
 
             childTestScope.Dispose();
 
-            Assert.Equal(email, rootTestScope.Span.GetTag(Tags.User.Email));
-            Assert.Equal(name, rootTestScope.Span.GetTag(Tags.User.Name));
-            Assert.Equal(id, rootTestScope.Span.GetTag(Tags.User.Id));
-            Assert.Equal(sessionId, rootTestScope.Span.GetTag(Tags.User.SessionId));
-            Assert.Equal(role, rootTestScope.Span.GetTag(Tags.User.Role));
-            Assert.Equal(scope, rootTestScope.Span.GetTag(Tags.User.Scope));
+            var traceContext = rootTestScope.Span.Context.TraceContext;
+            Assert.Equal(email, traceContext.Tags.GetTag(Tags.User.Email));
+            Assert.Equal(name, traceContext.Tags.GetTag(Tags.User.Name));
+            Assert.Equal(id, traceContext.Tags.GetTag(Tags.User.Id));
+            Assert.Equal(sessionId, traceContext.Tags.GetTag(Tags.User.SessionId));
+            Assert.Equal(role, traceContext.Tags.GetTag(Tags.User.Role));
+            Assert.Equal(scope, traceContext.Tags.GetTag(Tags.User.Scope));
         }
 
         [Fact]