Courts will look carefully at English-only rules to determine whether they are discriminatory and illegal. Because the language we speak is closely connected to our nationality, English-only rules may very well discriminate on the basis of national origin.

Generally, employers have to show that there is a business necessity for the policy. For example, if an employer can show that safety requires all workers to speak a common language, or that an English-only rule is necessary to serve customers who speak only English, that would constitute a business necessity.

Even if an employer has a good reason for requiring employees to speak English, however, it cannot adopt a policy that is too broad. For example, requiring employees to speak English to customers might pass muster; prohibiting employees from speaking any other language even while on breaks and making personal phone calls might not.

To learn more about English-only rules, take a look at Your Rights in the Workplace, by Barbara Kate Repa (Nolo).