Can my boss punish me for making a formal complaint about racism at work?

Based on the facts you provided, your employer's actions appear to constitute victimisation. Victimisation is when someone is treated badly because they made a complaint about discrimination [cite:au-racial-discrimination-1975-sec18aa]. According to the Racial Discrimination Act 1975, it is unlawful for a person to "commit an act of victimisation against another person" [cite:au-racial-discrimination-1975-sec18aa]. This means an employer cannot legally target you for reporting racism. Specifically, the law states that victimisation occurs if a person "prejudices, or threatens to prejudice, the other person in the other person’s employment; or intimidates or coerces, or imposes any pecuniary or other penalty upon, the other person" [cite:au-racial-discrimination-1975-sec18aa]. In your case, your supervisor's actions on 10 March—cutting your overtime shifts, removing your $1,200 bonus, and threatening your job security—could be seen as imposing a "pecuniary or other penalty" (a pecuniary penalty is a financial loss) and "prejudicing" your employment [cite:au-racial-discrimination-1975-sec18aa]. These actions happened "by reason that" you lodged a formal grievance on 15 February regarding the derogatory comments made by the senior manager [cite:au-racial-discrimination-1975-sec18aa]. Furthermore, the Fair Work Act 2009 prohibits employers from taking "adverse action" (unfavourable treatment) against an employee because of their race or other protected characteristics [cite:au-fair-work-2009-sec351]. While your supervisor claims your "attitude" is the problem, if the true reason for the change in treatment is your formal complaint, this is unlawful [cite:au-fair-work-2009-sec351]. It is currently uncertain whether the company can prove that the loss of overtime and the bonus was due to legitimate performance issues rather than retaliation for your complaint.