How does seniority play a role in how overtime is scheduled?

From the standpoint of the union:

Management shows favoritism and selectively chooses certain employees to get overtime.

Management takes away the overtime of workers when they get out there and start doing our jobs; we were hired to do a job and management keeps taking away our rights to overtime.

Questions that need to be answered in the discussion forum:

Should a supervisor (management) be allowed to work alongside an employee covered by the CBA and thereby minimize or eliminate the opportunity for employees to earn overtime?

Specifically, how should the overtime be distributed to ensure it is done in a fair and equitable manner?

If an overtime list is created, how should it be managed since there are certain workers qualified for some tasks but not others? Should there be several task specific lists created, or an overall shop list?

How does seniority play a role in how overtime is scheduled?