Having an “all-English-all-the-time” rule could land a company in a lot of trouble.
An Equal Employment Opportunity Commission (EEOC) regulation says requiring employees to speak only English at all times in the workplace is a burdensome term and condition of employment and violates Title VII of the Civil Rights Act of 1964. Therefore, a speak-English-only rule that applies to casual conversations between employees on break or not performing a job duty would be unlawful, according to guidance provided by the Department of Labor (DOL).
To be acceptable, an English-only rule must be narrowly tailored to address business necessity. Situations in which business necessity would justify such a rule include:
Communications with customers, coworkers, or supervisors who only speak English;
Emergencies or other situations in which employees must speak a common language to promote safety;
Cooperative work assignments in which the rule is needed to promote efficiency; or
Enabling a supervisor who only speaks English to monitor the performance of an employee.