The courts have decided that the Rehabilitation Act and the ADA do not overrule seniority systems or collective bargaining agreements. In major industries with strong unions, job placement is often based on union rules rather than employer choice. The employer makes the decision to hire an individual into a broad job category, but it is the shop rules that determine which specific job the individual is assigned. (The EEOC has announced that it believes the ADA should preempt collective bargaining agreements and that the court decisions to the contrary are incorrect, so this area of the law is subject to change.)

If this individual is disabled according to the ADA, the employer may be required to provide accommodations, but this does not include assigning the individual another job if that would violate union seniority rules. For example, the employer may be required to prevent smoking by team members if the individual is allergic to smoke. The employer is not required to move the employee to another team that has no smokers if this violates seniority or shop rules.

Although this seems unreasonable at times, there are sound reasons for maintaining a seniority system. As workers grow older, they tend to acquire arthritis, heart and lung disease, and a history of injuries, along with their seniority. These workers can use their seniority to bid into jobs that are less demanding physically. If ADA enforcement allowed new workers to bump workers with high seniority, these workers would have to declare their disabilities to keep the less stressful jobs. The result would be more aggravation for the established workers, but no more jobs for the individuals with disabilities.