Can accrued sick days be rescinded by an employer?

An employee is told that he may aculate not more than 20 sick days per year. This policy was in effect for 5 years and had been followed by both employee and employer. The employee has aculated 10 sick days but at the start of the next year the employer states that the sick day policy is no longer in effect and that he will not honor the employees already accrued 10 sick days. This is not a union employee so what action can be taken and what law has been broken if any?