Antonyms of adj nonmandatory

1 sense of nonmandatory

Sense 1
nonmandatory, nonobligatory -- (not required by rule or law)

INDIRECT (VIA optional) -> obligatory -- (morally or legally constraining or binding; "attendance is obligatory"; "an obligatory contribution")

Similarity of adj nonmandatory

1 sense of nonmandatory

Sense 1
nonmandatory, nonobligatory -- (not required by rule or law)
       => optional (vs. obligatory) -- (possible but not necessary; left to personal choice)