diff --git a/src/Runner.Common/Constants.cs b/src/Runner.Common/Constants.cs
index 4f8694d53..a5074b7e0 100644
--- a/src/Runner.Common/Constants.cs
+++ b/src/Runner.Common/Constants.cs
@@ -140,6 +140,9 @@ namespace GitHub.Runner.Common
 
             public static readonly string InternalTelemetryIssueDataKey = "_internal_telemetry";
             public static readonly string WorkerCrash = "WORKER_CRASH";
+            public static readonly string UnsupportedCommand = "UNSUPPORTED_COMMAND";
+            public static readonly string UnsupportedCommandMessage = "The `{0}` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/";
+            public static readonly string UnsupportedCommandMessageDisabled = "The `{0}` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/";
         }
 
         public static class RunnerEvent
@@ -198,6 +201,7 @@ namespace GitHub.Runner.Common
                 //
                 // Keep alphabetical
                 //
+                public static readonly string AllowUnsupportedCommands = "ACTIONS_ALLOW_UNSECURE_COMMANDS";
                 public static readonly string RunnerDebug = "ACTIONS_RUNNER_DEBUG";
                 public static readonly string StepDebug = "ACTIONS_STEP_DEBUG";
             }
diff --git a/src/Runner.Worker/ActionCommandManager.cs b/src/Runner.Worker/ActionCommandManager.cs
index be96a4514..0cd99e57b 100644
--- a/src/Runner.Worker/ActionCommandManager.cs
+++ b/src/Runner.Worker/ActionCommandManager.cs
@@ -1,4 +1,5 @@
 using GitHub.DistributedTask.Pipelines;
+using GitHub.DistributedTask.Pipelines.ContextData;
 using GitHub.DistributedTask.WebApi;
 using GitHub.Runner.Common.Util;
 using GitHub.Runner.Worker.Container;
@@ -183,6 +184,40 @@ namespace GitHub.Runner.Worker
 
         public void ProcessCommand(IExecutionContext context, string line, ActionCommand command, ContainerInfo container)
         {
+            var configurationStore = HostContext.GetService<IConfigurationStore>();
+            var isHostedServer = configurationStore.GetSettings().IsHostedServer;
+            
+            var allowUnsecureCommands = false;
+            bool.TryParse(Environment.GetEnvironmentVariable(Constants.Variables.Actions.AllowUnsupportedCommands), out allowUnsecureCommands);
+
+            // Apply environment from env context, env context contains job level env and action's env block
+#if OS_WINDOWS
+            var envContext = context.ExpressionValues["env"] as DictionaryContextData;
+#else
+            var envContext = context.ExpressionValues["env"] as CaseSensitiveDictionaryContextData;
+#endif
+            if (!allowUnsecureCommands && envContext.ContainsKey(Constants.Variables.Actions.AllowUnsupportedCommands))
+            {
+                bool.TryParse(envContext[Constants.Variables.Actions.AllowUnsupportedCommands].ToString(), out allowUnsecureCommands);
+            }
+
+            // TODO: Eventually remove isHostedServer and apply this to dotcom customers as well
+            if (!isHostedServer && !allowUnsecureCommands)
+            {
+                throw new Exception(String.Format(Constants.Runner.UnsupportedCommandMessageDisabled, this.Command));
+            }
+            else if (!allowUnsecureCommands)
+            {
+                // Log Telemetry and let user know they shouldn't do this
+                var issue = new Issue() 
+                { 
+                    Type = IssueType.Warning, 
+                    Message = String.Format(Constants.Runner.UnsupportedCommandMessage, this.Command)
+                };
+                issue.Data[Constants.Runner.InternalTelemetryIssueDataKey] = Constants.Runner.UnsupportedCommand;
+                context.AddIssue(issue);
+            }
+
             if (!command.Properties.TryGetValue(SetEnvCommandProperties.Name, out string envName) || string.IsNullOrEmpty(envName))
             {
                 throw new Exception("Required field 'name' is missing in ##[set-env] command.");
@@ -282,6 +317,40 @@ namespace GitHub.Runner.Worker
 
         public void ProcessCommand(IExecutionContext context, string line, ActionCommand command, ContainerInfo container)
         {
+            var configurationStore = HostContext.GetService<IConfigurationStore>();
+            var isHostedServer = configurationStore.GetSettings().IsHostedServer;
+            
+            var allowUnsecureCommands = false;
+            bool.TryParse(Environment.GetEnvironmentVariable(Constants.Variables.Actions.AllowUnsupportedCommands), out allowUnsecureCommands);
+
+            // Apply environment from env context, env context contains job level env and action's env block
+#if OS_WINDOWS
+            var envContext = context.ExpressionValues["env"] as DictionaryContextData;
+#else
+            var envContext = context.ExpressionValues["env"] as CaseSensitiveDictionaryContextData;
+#endif
+            if (!allowUnsecureCommands && envContext.ContainsKey(Constants.Variables.Actions.AllowUnsupportedCommands))
+            {
+                bool.TryParse(envContext[Constants.Variables.Actions.AllowUnsupportedCommands].ToString(), out allowUnsecureCommands);
+            }
+
+            // TODO: Eventually remove isHostedServer and apply this to dotcom customers as well
+            if (!isHostedServer && !allowUnsecureCommands)
+            {
+                throw new Exception(String.Format(Constants.Runner.UnsupportedCommandMessageDisabled, this.Command));
+            }
+            else if (!allowUnsecureCommands)
+            {
+                // Log Telemetry and let user know they shouldn't do this
+                var issue = new Issue() 
+                { 
+                    Type = IssueType.Warning, 
+                    Message = String.Format(Constants.Runner.UnsupportedCommandMessage, this.Command)
+                };
+                issue.Data[Constants.Runner.InternalTelemetryIssueDataKey] = Constants.Runner.UnsupportedCommand;
+                context.AddIssue(issue);
+            }
+
             ArgUtil.NotNullOrEmpty(command.Data, "path");
             context.Global.PrependPath.RemoveAll(x => string.Equals(x, command.Data, StringComparison.CurrentCulture));
             context.Global.PrependPath.Add(command.Data);