Employers considering an English-only policy in the workplace “need to be able to identify and explain what their business need is,” said Dennis Westlind, a partner with law firm Stoel & Rives L.L.P. in Portland, Ore.

If it is not a matter of customer service or assuring safety, then “it's a pretty good indicator you shouldn't have a policy,” Mr. Westlind said.

“If an English-only policy is not necessary, don't adopt one,” said Michael P. Burns, an associate with law firm Horan, Lloyd, Karachale, Dyer, Schwartz, Law & Cook Inc. in Monterey, Calif. “It's usually better to stay out of this hornet's nest than to go into it unnecessarily.”

Any policy should be “carefully implemented, carefully worded and carefully followed” to avoid violating federal law, said Leslie Silverman, a partner with law firm Proskauer Rose L.L.P. in Washington and a former vice chair at the Equal Employment Opportunity Commission.

In some cases, said Ernest Haffner, senior EEOC attorney adviser, employers have adopted English-only policies that were “just a little bit broader than they needed to be.”

James A. Matthews III, a partner with Fox Rothschild L.L.P. in Philadelphia, said if a policy is called for, “common sense suggests you would try to tailor the rule as narrowly as possible to address the problem you've indentified and not necessarily try to kill a flea with a sledgehammer.”

If customers should complain that employees are “standing in front of them speaking a language they don't understand,” which makes them feel uncomfortable, the question to ask is: “Do you need to promulgate a blanket English-only rule anytime, anywhere in the workplace,” Mr. Matthews said, “or do you want to promulgate a rule that you'll speak English in business areas of the store when customers are present?”

Aaron R. Gelb, a shareholder with law firm Vedder Price P.C. in Chicago, said one case he was involved in concerned a bank teller who lodged a complaint with the EEOC for being reprimanded for speaking a foreign language with another bank employee in front of a customer.

The EEOC, however, did not pursue the matter. “There was no overreaching on the part of the employer to say, "You don't speak your language on breaks,'” Mr. Gelb said. Instead, the employer's “measured response” to a customer's discomfort “kept them out of the crosshairs” of the EEOC.