If you’ve ever dined at Chinese chain P.F. Chang’s, you or someone you were with might have been excited by their gluten-free menu: From Singapore noodles to Mongolian beef to the flourless chocolate cake, nothing is more delightful for someone with dietary restrictions than a full menu of food they can eat. Many happily pay the extra charges Chang’s and other restaurants add to gluten-free bills.

But according to a class action lawsuit filed in California and kicked up to Federal court, those extra charges are a violation of the Americans with Disabilities Act.

You see, the ADA states “public accommodation may not impose a surcharge on a particular individual with a disability or any group of individuals with disabilities to cover the costs of measures.”

In other words, Chang’s is in violation of the ADA, the lawsuit alleges, by charging more to only those people with the disability: the inability to healthfully consume gluten, whether celiac or any number of other diseases identified with gluten sensitivity, such as Crohn’s or Ulcerative Colitis.

“With disability discrimination, people are discriminated against in ways that might not be obvious,” says Josh Glickman, attorney at the Social Justice Law Collective, a firm that specializes in housing, disability, and incarceration issues. (He is not involved in the Chang’s case.) “It goes beyond structural and design accommodations. People feel that the ADA is about ramps and structural design, but people are being discriminated against in a variety of ways that may not be obvious.”

Glickman notes that people with food allergies are covered under the ADA “when that food allergy substantially limits a major life activity.”

The suit points out that the ADA explicitly says establishments must provide accommodation for persons with disabilities, including “special foods to meet particular dietary needs.”

The suit also states, “if an establishment already makes alterations or modifications, or takes special orders for its customers, it must do so for disabled customer requests as well.”

Because a gluten-free diet is, for many, a medical necessity, the suit says charging those people extra is discriminatory.

“When you’re looking at the context of reasonable accommodation [in the ADA], the law says you can’t pass that cost on,” says Glickman. “It doesn’t matter if it’s 50 cents or five dollars—they can’t pass that cost on to only those people dining with the disability.”

Glickman says, “It is never okay to pass the cost of [ADA] compliance to those who are actually suffering from disabilities. When you go to a movie theater, if you are hearing impaired, you get an accessibility device.”

What Chang’s is doing, he notes, is like a movie theater charging an extra dollar or two to every person requiring the hearing device.

Yet many people with gluten issues are now accustomed to paying extra in restaurants for food they can eat. Glickman says if all establishments like movie theaters and public venues started passing their costs of ADA compliance to only the disabled, reaction to this issue “would look much different.”

The lawsuit points out that many items on the regular Chang’s menu might be gluten-free, yet when ordered off the gluten-free menu they incur the extra charge.

The plaintiffs seek an injunction to stop extra charges on gluten-free orders for people with celiac or gluten sensitivities, along with compensation.

Notes Glickman: “It comes down to who pays. Disability discrimination does not end with ensuring handicap accessible bathrooms and constructing ramped entrances into buildings. Lawsuits such as this are important because they educate consumers, disease sufferers, and food providers of the requirements of the ADA, and help ensure that people with disabilities are not discriminated against in violation of the law.”

Attorneys for P.F. Chang’s declined to comment and attorneys for the plaintiffs did not respond to numerous requests for comment.