It depends whether the bonus in question is “discretionary,” or a part of your agreed-upon wages.
If the bonus is discretionary, it means your employer can decide whether to give you a bonus or not for any reason- or no reason- at all. Often these bonuses are based on company performance or are given as gifts around the holidays. Generally speaking, you have no legal recourse if your employer decides to decrease or take away a discretionary bonus.
However, many employers provide formulas for bonuses based on some concrete metrics and they are contractually guaranteed. If this is the case, you can sometimes bring a cause of action against your employer for failing to pay wages or breach of contract. One other issue to look out for us whether the employee’s wage falls below the minimum wage without the bonus.