--- a/taskcluster/taskgraph/action.py
+++ b/taskcluster/taskgraph/action.py
@@ -4,16 +4,17 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 import json
 import logging
 import requests
+import yaml
 
 from .create import create_tasks
 from .decision import write_artifact
 from .parameters import Parameters
 from .optimize import optimize_task_graph
 from .taskgraph import TaskGraph
 
 logger = logging.getLogger(__name__)
@@ -28,29 +29,31 @@ def taskgraph_action(options):
      * creating taskgraph of tasks asked for in parameters with respect to
      a given gecko decision task and schedule these jobs.
     """
 
     parameters = get_action_parameters(options)
     decision_task_id = parameters['decision_id']
     # read in the full graph for reference
     full_task_json = get_artifact(decision_task_id, "public/full-task-graph.json")
+    decision_params = get_artifact(decision_task_id, "public/parameters.yml")
     all_tasks, full_task_graph = TaskGraph.from_json(full_task_json, options['root'])
 
     target_tasks = set(parameters['task_labels'].split(','))
     target_graph = full_task_graph.graph.transitive_closure(target_tasks)
     target_task_graph = TaskGraph(
         {l: all_tasks[l] for l in target_graph.nodes},
         target_graph)
 
     existing_tasks = get_artifact(decision_task_id, "public/label-to-taskid.json")
 
     # We don't want to optimize target tasks since they have been requested by user
     # Hence we put `target_tasks under` `do_not_optimize`
     optimized_graph, label_to_taskid = optimize_task_graph(target_task_graph=target_task_graph,
+                                                           params=decision_params,
                                                            do_not_optimize=target_tasks,
                                                            existing_tasks=existing_tasks)
 
     # write out the optimized task graph to describe what will actually happen,
     # and the map of labels to taskids
     write_artifact('task-graph.json', optimized_graph.to_json())
     write_artifact('label-to-taskid.json', label_to_taskid)
     # actually create the graph
@@ -67,10 +70,13 @@ def get_action_parameters(options):
     ] if n in options}
 
     return Parameters(parameters)
 
 
 def get_artifact(task_id, path):
     url = TASKCLUSTER_QUEUE_URL + task_id + "/artifacts/" + path
     resp = requests.get(url=url)
-    artifact = json.loads(resp.text)
+    if path.endswith('.json'):
+        artifact = json.loads(resp.text)
+    elif path.endswith('.yml'):
+        artifact = yaml.load(resp.text)
     return artifact