diff --git a/server/core/internal/worker.hh b/server/core/internal/worker.hh
index 452914f4f..1963d3bb4 100644
--- a/server/core/internal/worker.hh
+++ b/server/core/internal/worker.hh
@@ -14,6 +14,7 @@
 
 #include <maxscale/cppdefs.hh>
 #include <map>
+#include <tr1/unordered_set>
 #include <memory>
 #include <maxscale/platform.h>
 #include <maxscale/session.h>
@@ -1296,20 +1297,23 @@ private:
         }
     };
 
-    typedef DelegatingTimer<Worker> PrivateTimer;
-    typedef std::multimap<int64_t, DelayedCall*> DelayedCalls;
+    typedef DelegatingTimer<Worker>                         PrivateTimer;
+    typedef std::tr1::unordered_set<DelayedCall*>           DelayedCalls;
+    typedef std::multimap<int64_t, DelayedCall*>            DelayedCallsByTime;
+    typedef std::tr1::unordered_map<intptr_t, DelayedCalls> DelayedCallsByTag;
 
-    STATISTICS    m_statistics;           /*< Worker statistics. */
-    MessageQueue* m_pQueue;               /*< The message queue of the worker. */
-    THREAD        m_thread;               /*< The thread handle of the worker. */
-    bool          m_started;              /*< Whether the thread has been started or not. */
-    bool          m_should_shutdown;      /*< Whether shutdown should be performed. */
-    bool          m_shutdown_initiated;   /*< Whether shutdown has been initated. */
-    uint32_t      m_nCurrent_descriptors; /*< Current number of descriptors. */
-    uint64_t      m_nTotal_descriptors;   /*< Total number of descriptors. */
-    Load          m_load;                 /*< The worker load. */
-    PrivateTimer* m_pTimer;               /*< The worker's own timer. */
-    DelayedCalls  m_delayed_calls;        /*< Current delayed calls. */
+    STATISTICS         m_statistics;           /*< Worker statistics. */
+    MessageQueue*      m_pQueue;               /*< The message queue of the worker. */
+    THREAD             m_thread;               /*< The thread handle of the worker. */
+    bool               m_started;              /*< Whether the thread has been started or not. */
+    bool               m_should_shutdown;      /*< Whether shutdown should be performed. */
+    bool               m_shutdown_initiated;   /*< Whether shutdown has been initated. */
+    uint32_t           m_nCurrent_descriptors; /*< Current number of descriptors. */
+    uint64_t           m_nTotal_descriptors;   /*< Total number of descriptors. */
+    Load               m_load;                 /*< The worker load. */
+    PrivateTimer*      m_pTimer;               /*< The worker's own timer. */
+    DelayedCallsByTime m_delayed_calls;        /*< Current delayed calls ordered by time. */
+    DelayedCallsByTag  m_tagged_calls;         /*< Current delayed calls ordered by tag. */
 };
 
 }
diff --git a/server/core/worker.cc b/server/core/worker.cc
index 748827aba..f1f994657 100644
--- a/server/core/worker.cc
+++ b/server/core/worker.cc
@@ -1141,12 +1141,22 @@ void Worker::tick()
 
         m_delayed_calls.erase(i++);
 
+        ss_dassert(m_tagged_calls.find(pDelayed_call->tag()) != m_tagged_calls.end());
+
+        DelayedCalls& delayed_calls = m_tagged_calls[pDelayed_call->tag()];
+
+        auto j = delayed_calls.find(pDelayed_call);
+        ss_dassert(j != delayed_calls.end());
+
         if (pDelayed_call->call(Worker::Call::EXECUTE))
         {
             repeating_calls.push_back(pDelayed_call);
         }
         else
         {
+            // If the call is not repeated, we remove it from the set
+            // associated with the tag.
+            delayed_calls.erase(j);
             delete pDelayed_call;
         }
     }
@@ -1178,8 +1188,15 @@ void Worker::add_delayed_call(DelayedCall* pDelayed_call)
         }
     }
 
+    // Insert the delayed call into the map ordered by invocation time.
     m_delayed_calls.insert(std::make_pair(pDelayed_call->at(), pDelayed_call));
 
+    // Insert the delayed call into the set associated with the tag of
+    // the delayed call.
+    DelayedCalls& delayed_calls = m_tagged_calls[pDelayed_call->tag()];
+    ss_dassert(delayed_calls.find(pDelayed_call) == delayed_calls.end());
+    delayed_calls.insert(pDelayed_call);
+
     if (adjust)
     {
         adjust_timer();
@@ -1210,9 +1227,58 @@ void Worker::adjust_timer()
 
 int32_t Worker::cancel_delayed_calls(intptr_t tag)
 {
-    // TODO: Implement
-    ss_dassert(!true);
-    return 0;
+    int n = 0;
+
+    auto i = m_tagged_calls.find(tag);
+
+    if (i != m_tagged_calls.end())
+    {
+        // All delayed calls associated with the provided tag.
+        DelayedCalls& delayed_calls = i->second;
+        ss_debug(int nDelayed_calls = delayed_calls.size());
+
+        for (auto j = delayed_calls.begin(); j != delayed_calls.end(); ++j)
+        {
+            DelayedCall* pDelayed_call = *j;
+
+            // All delayed calls with exactly the same trigger time.
+            // Not particularly likely there will be many of those.
+            auto range = m_delayed_calls.equal_range(pDelayed_call->at());
+
+            auto k = range.first;
+            ss_dassert(k != range.second);
+            ss_debug(bool found = false);
+
+            while (k != range.second)
+            {
+                if (k->second == pDelayed_call)
+                {
+                    m_delayed_calls.erase(k);
+                    delete pDelayed_call;
+                    ++n;
+
+                    k = range.second;
+
+                    ss_debug(found = true);
+                }
+                else
+                {
+                    ++k;
+                }
+            }
+
+            ss_dassert(found);
+        }
+
+        ss_dassert(nDelayed_calls == n);
+    }
+    else
+    {
+        ss_dassert(!true);
+        MXS_WARNING("Attempt to remove calls associated with non-existing tag.");
+    }
+
+    return n;
 }
 
 }