No, you cannot sue them, based on what you write. You don't indicate that they refuse to let you go generally--just that the desk must be covered. An employer's obligation regarding an employee's medical condition or needs is to make "reasonable accommodations" to them. It is reasonable to require a receptionist desk to be covered before the receptionist leaves it--that is simply the nature of the job. There will be times when coverage is temporarily unvailable, but that does not make the policy unreasonable, and so they are not guilty of not making a reasonable accommodation. You are not being discriminated against--you are the receptionist, and a receptionist job is different than, say, being IT or a copyeditor or file clerk or graphic artist, etc. People may be treated differently due to the demands of their job, and that is not illegal. If you are subject to frequent or urgent needs to go to the bathroom, than it is possible that you may need to look for a different job, one where you can leave the position uncovered at will or need.