Can we as union members be asked to sign a "Statement on a Drug Free Workplace" if it hasn't been negotiated in collective bargaining?

Union members may be asked to do anything which is not barred--or at least addressed--by a collective bargaining contract. For example, if a collective bargaining agreement does not set hours or shifts, the employer is free to set the hours and shifts as it likes. Therefore, if the contract is silent about these statements, employees can be asked to sign them; however, if the contract limits the grounds for discipline or termination, the company may be limited in the actions it can take against employees who refuse to sign them--the company could only take actions which comport with the contract's terms.