Unfortunately, not only at will employees but sometimes union employees get caught in a situation where a shift is eliminated or the company switches to different hours. Many times even union contracts do not address how to protect the employees on the eliminated shift. A union or contract employee may be able to rely on a seniority clause in his or her contract, but at will employees are not protected.
The reality is that many times employees affected by a shift being eliminated or hours being changed are young mothers who must arrange their work hours in order to obtain child care. There is no law in the United States that gives additional rights to parents so they can reschedule hours around day care or child care. This type of change can also affect those who work two jobs and those who attend school.
Just as in the changing of job responsibilities, changing of hours or shift elimination cannot be done for discriminatory reasons. Also, like other legal disputes, this action may only be settled in court. Be warned however, the employer will swear and produce evidence that this type of change was done solely due to economic and business reasons. The EEOC does recognize economic and business reasons as legitimate arguments against discrimination.