diff --git a/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentEditController.php b/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentEditController.php
--- a/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentEditController.php
+++ b/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentEditController.php
@@ -31,6 +31,25 @@
 
     $done_uri = $obj_handle->getURI();
 
+    // If an object is locked, you can't edit comments on it. Two reasons to
+    // lock threads are to calm contentious issues and to freeze state for
+    // auditing, and editing comments serves neither goal.
+
+    $object = $xaction->getObject();
+    $can_interact = PhabricatorPolicyFilter::hasCapability(
+      $viewer,
+      $object,
+      PhabricatorPolicyCapability::CAN_INTERACT);
+    if (!$can_interact) {
+      return $this->newDialog()
+        ->setTitle(pht('Conversation Locked'))
+        ->appendParagraph(
+          pht(
+            'You can not edit this comment because the conversation is '.
+            'locked.'))
+        ->addCancelButton($done_uri);
+    }
+
     if ($request->isFormOrHisecPost()) {
       $text = $request->getStr('text');
 
diff --git a/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentRemoveController.php b/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentRemoveController.php
--- a/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentRemoveController.php
+++ b/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentRemoveController.php
@@ -32,6 +32,26 @@
 
     $done_uri = $obj_handle->getURI();
 
+    // We allow administrative removal of comments even if an object is locked,
+    // so you can lock a flamewar and then go clean it up. Locked threads may
+    // not otherwise be edited, and non-administrators can not remove comments
+    // from locked threads.
+
+    $object = $xaction->getObject();
+    $can_interact = PhabricatorPolicyFilter::hasCapability(
+      $viewer,
+      $object,
+      PhabricatorPolicyCapability::CAN_INTERACT);
+    if (!$can_interact && !$viewer->getIsAdmin()) {
+      return $this->newDialog()
+        ->setTitle(pht('Conversation Locked'))
+        ->appendParagraph(
+          pht(
+            'You can not remove this comment because the conversation is '.
+            'locked.'))
+        ->addCancelButton($done_uri);
+    }
+
     if ($request->isFormOrHisecPost()) {
       $comment = $xaction->getApplicationTransactionCommentObject()
         ->setContent('')
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionCommentEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionCommentEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionCommentEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionCommentEditor.php
@@ -189,6 +189,10 @@
         $actor,
         $xaction,
         PhabricatorPolicyCapability::CAN_EDIT);
+      PhabricatorPolicyFilter::requireCapability(
+        $actor,
+        $xaction->getObject(),
+        PhabricatorPolicyCapability::CAN_INTERACT);
     }
   }
 
diff --git a/src/applications/transactions/view/PhabricatorApplicationTransactionView.php b/src/applications/transactions/view/PhabricatorApplicationTransactionView.php
--- a/src/applications/transactions/view/PhabricatorApplicationTransactionView.php
+++ b/src/applications/transactions/view/PhabricatorApplicationTransactionView.php
@@ -505,12 +505,19 @@
         if ($has_edit_capability && !$has_removed_comment) {
           $event->setIsEditable(true);
         }
+
         if ($has_edit_capability || $viewer->getIsAdmin()) {
           if (!$has_removed_comment) {
             $event->setIsRemovable(true);
           }
         }
       }
+
+      $can_interact = PhabricatorPolicyFilter::hasCapability(
+        $viewer,
+        $xaction->getObject(),
+        PhabricatorPolicyCapability::CAN_INTERACT);
+      $event->setCanInteract($can_interact);
     }
 
     $comment = $this->renderTransactionContent($xaction);
diff --git a/src/view/phui/PHUITimelineEventView.php b/src/view/phui/PHUITimelineEventView.php
--- a/src/view/phui/PHUITimelineEventView.php
+++ b/src/view/phui/PHUITimelineEventView.php
@@ -32,6 +32,7 @@
   private $isSilent;
   private $isMFA;
   private $isLockOverride;
+  private $canInteract;
 
   public function setAuthorPHID($author_phid) {
     $this->authorPHID = $author_phid;
@@ -114,6 +115,15 @@
     return $this->isEditable;
   }
 
+  public function setCanInteract($can_interact) {
+    $this->canInteract = $can_interact;
+    return $this;
+  }
+
+  public function getCanInteract() {
+    return $this->canInteract;
+  }
+
   public function setIsRemovable($is_removable) {
     $this->isRemovable = $is_removable;
     return $this;
@@ -650,6 +660,10 @@
   private function getMenuItems($anchor) {
     $xaction_phid = $this->getTransactionPHID();
 
+    $can_interact = $this->getCanInteract();
+    $viewer = $this->getViewer();
+    $is_admin = $viewer->getIsAdmin();
+
     $items = array();
 
     if ($this->getIsEditable()) {
@@ -658,6 +672,7 @@
         ->setHref('/transactions/edit/'.$xaction_phid.'/')
         ->setName(pht('Edit Comment'))
         ->addSigil('transaction-edit')
+        ->setDisabled(!$can_interact)
         ->setMetadata(
           array(
             'anchor' => $anchor,
@@ -727,17 +742,23 @@
       $items[] = id(new PhabricatorActionView())
         ->setType(PhabricatorActionView::TYPE_DIVIDER);
 
-      $items[] = id(new PhabricatorActionView())
+      $remove_item = id(new PhabricatorActionView())
         ->setIcon('fa-trash-o')
         ->setHref('/transactions/remove/'.$xaction_phid.'/')
         ->setName(pht('Remove Comment'))
-        ->setColor(PhabricatorActionView::RED)
         ->addSigil('transaction-remove')
         ->setMetadata(
           array(
             'anchor' => $anchor,
           ));
 
+      if (!$is_admin && !$can_interact) {
+        $remove_item->setDisabled(!$is_admin && !$can_interact);
+      } else {
+        $remove_item->setColor(PhabricatorActionView::RED);
+      }
+
+      $items[] = $remove_item;
     }
 
     return $items;