nonmandatory

attending the optional workshop is nonmandatory, but highly recommended.

the safety briefing was nonmandatory for experienced pilots.

wearing a helmet during the bike tour was nonmandatory.

volunteering for the project is nonmandatory, but greatly appreciated.

the overtime hours are nonmandatory, and employees can decline them.

contributing to the fundraising campaign is nonmandatory for all staff.

the introductory session on the software was nonmandatory.

participating in the team-building activity was nonmandatory.

bringing your own lunch is nonmandatory; the cafeteria is open.

attending the holiday party is nonmandatory, but festive cheer is encouraged.

submitting a proposal is nonmandatory, but can enhance your visibility.