Article 30.2.P
P. Sunday Work
An office-wide list will be established for substitutes, rural
carrier associates, and rural carrier relief employees who
desire to work on Sunday. When there is a need to work
leave replacements on Sunday, the Employer may require a
part-time flexible rural carrier work prior to selecting qualified
employees from the list. The Employer will make every
reasonable effort to avoid requiring substitutes, RCAs, and
RCRs not on the list to work.
https://www.ruralinfo.net/wp-content/uploads/2017/04/2015-2018-National-Agreement.pdf
There is also this:
<img src="https://www.knowledgebase.ruralinfo.net/wp-content/uploads/2016/06/sunlist.jpg" width="1600" alt="sunlist.jpg" />