Is it illegal for an employer to enforce an English only policy in the workplace?

In most circumstances, it is illegal for an employer to require employees to speak only English in the workplace. One of the rare exceptions to the rule is if speaking another language may create a hazardous condition to the workers or the public. But even then, English only should be implemented if there are no other reasonable alternatives. Employers are not required to impose English only policies because some employees may find the use of other languages to be exclusionary, distracting, rude and unprofessional. It is an invitation to a discrimination lawsuit. The best way to approach it is to treat the matter just as you would if any employee was behaving in a rude or unprofessional manner. Explain what that employee is doing that you believe is rude or unprofessional to a manager and let management handle it in an appropriate way.

I agree with my colleague who is an experienced employment attorney here in California. I would only add that you should be cautious. Base the way you approach this with common sense and how good of a relationship you have with your supervisor. I say that because there may be unwanted repercussions from your complaint. For instance, if your co-workers hear about your complaint, some of them may start treating you differently or talking about you (obviously in their native language). You may also experience some adverse treatment in other ways. I don't mean to rain on your parade but it is good to approach these sensitive issues with your eyes wide open. Be aware of both the potential you'll get what you want and also that you may not. Good luck.

You have received good answers. If it were me, I would try to start learning their language. Making a good attempt at speaking their language may well endear you to these other workers. You might even ask them for assistance. Just a thought....