First, as a general matter, forget about the idea that a hard working employee deserves a promotion; there is no legal right or entitlement to a promotion whatsoever, and employers never have to promote you.An employer cannot, however, discriminate against an employee, or treat him worse (including fewer opportunities) than other employees due to a disability. You may have a discrimination case if--1) You can do the job with your hearing condition. If the nature of the supervisor job is that with your level of hearing (including whatever hearing aids, etc. you use), you could not do the job effectively, they do not need to offer it to you. They do not need to compromise productivity, quality, or safety to accomodate you.2) You have whatever non-disability-related education, degrees, certification, experience, is required for the job; no matter what, you must be qualified for the job.3) You are as or more qualified than the people they did hire or promote for that position: they are allowed to go with the best candidate.4) There is no other reason you would not be promoted othet than your hearing--i.e. no poor performance reviews, no absenteeism, etc. They could you deny you a promotion for the same reasons they could deny it to anyone.If the answers to all four questions above is "yes," so that yiu could do the job with your hearing but nonetheless were denied it only because of your hearing, you may have a discrimination case. In that event, contact the EEOC to file a complaint.