Federal equal employment opportunity laws do not prohibit employers from changing their paid sick leave policy if it is done in a manner that does not discriminate between employees because of race, sex, age (40 and over), color, religion, national origin, disability or veteran status. Be sure also to consult state and local laws.
If your workforce is represented by a labor union and the collective bargaining agreement covers sick leave policies, you may be limited in either the manner in which you change the policy or the changes themselves because the collective bargaining agreement would be controlling. In a workplace without a collective bargaining agreement, employees may have a contractual right to any accrued sick leave, but not future leave.
Your sick leave policy also has to follow the requirements of the Family and Medical Leave Act (if your employees are covered by the Act), and it needs to be consistent with the federal workplace anti-discrimination laws, such as the Americans with Disabilities Act.
Source: U.S. Department of Labor, Wage and Hour Division’s “Pandemic Flu and Family and Medical Leave Act: Questions and Answers.”