Actually, in the absence of an employment contract guarantying you the right to that day off or otherwise limiting the grounds for discipline, you could have been fired for cause for not coming in when called. When there is no contract setting days, hours, or shifts, the employer determines those at its sole discretion and can change them at will, calling employees in on their days off. If the employee refuses, he disobeyed company directives and was absent from work without authorization, and is subject to any discipline up to and including termination for cause.