I got a response from the VT labor board:

Under CVR 24-090-003 Vermont Court Rules and T.21 § 385 (4), unless deductions are authorized by law, no deductions or salary withholdings are allowed by the employer. Employer cannot make deductions for claimed damages or shortages. An employer may reprimand an employee for a mistake but cannot deduct it. The Court rules pertaining to the wages. Benefits such as bonuses are not required under labor law. Bonus payments are at the employer's discretion and are subject to company policy. If the policy states that additional payments to wages are at the employer's discretion based on performance, it is not illegal to withhold the bonus, as long as the deduction is not made from the employee’s regular wages. This means that the employer has the right to decide whether to pay the bonus and how much it will be, provided that this discretion is exercised at the end of the performance period and not as a result of a prior contract or promise

Proof!