After Control-M determines which service class to assign to the job, but immediately before the service class is about to be set or reset (even if Control-M will not set any service class), Control-M calls user exit 20. The user exit is passed the following information:

• 8-character function code (JOBINIT, AFTDUEIN, or AFDUEOUT)
• pointer to job name
• pointer to MCT
• pointer to MIT
• pointer to start of the internal WLMSCTBL table (if the table exists)
• service class to be set or blanks
• pointer to the matched internal WLMSCTBL table entry (if the table exists and if a table entry actually matched the current job)

The user exit may change the service class. After returning to Control-M, the service class is checked. If it is non-blank or blank, Control-M will either issue or not issue the appropriate E operator command or WLM macro, to set or reset the service class.