CA Identity Portal can identify pending work items either as approvals (default) or implementations. In order for a work item to enter the implementations queue a hint needs to be configured on that node.
To configure the hint in CA Identity Manager:
CA Identity Portal\ CA Identity Suite 14.x
The Reject button is only available in Approval workflows (default), if you set the workflow to Implementation mode (ie IS_IMPLEMENTATION_NODE = True) the reject button will not be available