If your disciplining of employees went beyond counseling, guidance, coaching, and advice, and involved the application of disciplinary action, then there is no better term to use than "disciplined": It is a strong verb, that speaks "loud and clear."

If it sounds a bit too harsh to you, then you may want to smooth it in by using such an innocuous verb as "administered," acting upon an equally innocuous noun like "action," with the idea of "discipline" thrown in merely as a qualifier. This kind of padding is somtimes helpful in softening the impact of harsh expressions.

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