Antonyms for the phrase "of own free will" would be terms indicating the absence of free choice, such as "coerced," "forced," or "compelled." Compulsion denotes an action that is taken under pressure or out of necessity, often lacking any sense of control. Some other antonyms may be "involuntary," "obliged," or "constrained," all of which suggest a lack of autonomy or agency. These words can be used in the context of various situations, from legal issues to personal preferences, to describe actions that are taken without genuine consent or willingness. Therefore, antonyms of "of own free will" convey a different sentiment altogether.