Morales, who speaks only English, owns and operates a large warehouse. Most of his workers speak only English, and he requires that all of his employees speak English and that all communication in the workplace, which involves the performance of any job, be done in English. A number of workers whose primary language is not English complain about the policy on the grounds that they can converse in their native languages and still get the job done. If these employees bring a claim of national origin discrimination on the basis of this policy, what is Morales' best defense? describe.