Union challenges to drug testing under collective bargaining agreements are discussed in detail, with special emphasis on probable or reasonable cause standards and adequate notice. Reasonable and accurate testing procedures and privacy issues are outlined, as in the required relationship between the employee's drug use and the employer's business interests. Issues of employee termination and union options when the collective bargaining agreement is silent on drug testing are also discussed. Arbitrators will play a major role in defining permissible drug testing procedures and policies in unionized workplaces. 143 footnotes.