1. How does the Court answer the question “Does the ADA require an employer to assign a disabled employee to a particular position even though another employee is entitled to that position under the employer’s established seniority system?”
2. Explain the special circumstances exception. Who has the burden of proof to show special circumstances?

[After respondent Robert Barnett injured his back while he was a cargo handler for petitioner U.S. Airways, Inc., he transferred to a less physically demanding mailroom position. His new position later became open to seniority-based employee bidding under U.S. Airways' seniority system, and employees senior to him planned to bid on the job. U.S. Airways refused Barnett's request to accommodate his disability by allowing him to remain in the mailroom, and he lost his job. He then filed suit under the ADA, which prohibits an employer from discriminating against "an individual with a disability" who, with "reasonable accommodation," can perform a job's essential functions, unless the employer "can demonstrate that the accommodation would impose an undue hardship on the operation of [its] business." Finding that altering a seniority system would result in an "undue hardship" to both U.S. Airways and its nondisabled employees, the district court granted the company summary judgment. The Ninth Circuit reversed, holding that the seniority system was merely a factor in the undue hardship analysis and that a case-by-case, fact-intensive analysis is required to determine whether any particular assignment would constitute an undue hardship. The Supreme Court agreed to hear the case.]
BREYER, J.…
I.
In answering the question presented, we must consider the following statutory provisions. First, the ADA says that an employer may not "discriminate against a qualified individual with a disability." Second, the ADA says that a "qualified" individual includes "an individual with a disability who, with or without reasonable accommodation, can perform the essential functions of" the relevant "employment position." § 12111(8) (emphasis added). Third, the ADA says that "discrimination" includes an employer's "not making reasonable accommodations to the known physical or mental limitations of an otherwise qualified … employee, unless [the employer] can demonstrate that the accommodation would impose an undue hardship on the operation of
[its] business." § 12112(b)(5)(A) (emphasis added). Fourth, the ADA says that the term "'reasonable accommodation' may include … reassignment to a vacant position." § 12111(9)(B)….
II.
The question in the present case focuses on the relationship between seniority systems and the plaintiff's need to show that an "accommodation" seems reasonable on its face, i.e., ordinarily or in the run of cases. We must assume that the plaintiff, an employee, is an "individual with a disability." He has requested assignment to a mailroom position as a "reasonable accommodation." We also assume that normally such a request would be reasonable within the meaning of the statute, were it not for one circumstance, namely, that the assignment would violate the rules of a seniority system. See § 12111(9) ("reasonable accommodation" may include "reassignment to a vacant position"). Does that circumstance mean that the proposed accommodation is not a "reasonable" one?

In our view, the answer to this question ordinarily is "yes." The statute does not require proof on a caseby case basis that a seniority system should prevail. That is because it would not be reasonable in the run of cases that the assignment in question trump the rules of a seniority system. To the contrary, it will ordinarily be unreasonable for the assignment to prevail.
A
Several factors support our conclusion that a proposed accommodation will not be reasonable in the run of cases. Analogous case law supports this conclusion, for it has recognized the importance of seniority to employee-management relations…. Most important for present purposes, to require the typical employer to show more than the existence of a seniority system might well undermine the employees' expectations of consistent, uniform treatment-expectations upon which the seniority system's benefits depend. That is because such a rule would substitute a complex case-specific "accommodation" decision made by management for the more uniform, impersonal operation of seniority rules. Such management decisionmaking, with its inevitable discretionary elements, would involve a matter of the greatest importance to employees, namely, layoffs; it would take place outside, as well as inside, the confines of a court case; and it might well take place fairly often. Cf. ADA, 42 U.S.C. § 12101(a)(1), (estimating that some 43 million Americans suffer from physical or mental disabilities). We can find nothing in the statute that suggests Congress intended to undermine seniority systems in this way. And we consequently conclude that the employer's showing of violation of the rules of a seniority system is by itself ordinarily sufficient.
B
The plaintiff (here the employee) nonetheless remains free to show that special circumstances warrant a finding that, despite the presence of a seniority system (which the ADA may not trump in the run of cases), the requested "accommodation" is "reasonable" on the particular facts. That is because special circumstances might alter the important expectations described above…. The plaintiff might show, for example, that the employer, having retained the right to change the seniority system unilaterally, exercises that right fairly frequently, reducing employee expectations that the system will be followed-to the point where one more departure, needed to accommodate an individual with a disability, will not likely make a difference. The plaintiff might show that the system already contains exceptions such that, in the circumstances, one further exception is unlikely to matter. We do not mean these examples to exhaust the kinds of showings that a plaintiff might make. But we do mean to say that the plaintiff must bear the burden of showing special circumstances that make an exception from the seniority system reasonable in the particular case. And to do so, the plaintiff must explain why, in the particular case, an exception to the employer's seniority policy can constitute a "reasonable accommodation" even though in the ordinary case it cannot.
III.
In its question presented, U.S. Airways asked us whether the ADA requires an employer to assign a disabled employee to a particular position even though another employee is entitled to that position under the employer's "established seniority system." We answer that ordinarily the ADA does not require that assignment. Hence, a showing that the assignment would violate the rules of a seniority system warrants summary judgment for the employer-unless there is more. The plaintiff must present evidence of that "more," namely, special circumstances surrounding the particular case that demonstrate the assignment is nonetheless reasonable….
[W]e vacate the Court of Appeals' judgment and remand the case for further proceedings consistent with this opinion.
It is so ordered.