Giving employee the Sabbath day off: When is it an ‘undue hardship’?

Federal religious discrimination law (Title VII) says employers are obligated to “reasonably accommodate” an employee’s religious belief and practices, unless doing so would cause an “undue hardship” to the organization. In this case, accommodating an employee’s request for every Sabbath day off could effectively invalidate a collective-bargaining seniority system and create a real hardship for the other employees who would have to work instead.