Visuals Unlimited, Inc./Nucleus Medical Media via Getty Images

This week, the Food and Drug Administration (FDA) sent a warning letter to the Southern California marketing company 1-800-GET-THIN for using misleading advertising to promote Lap-Band weight-loss surgery.

The agency says the company’s numerous billboards feature thin models and enticing slogans like “Let Your New Life Begin!” but fail to convey the serious risks carried by weight-loss surgery. The warnings are there, but in font so small as to be illegible, the agency says. The FDA also took issue with 1-800-GET-THIN’s other marketing materials, which similarly do not inform patients about the risks.

The FDA letters — sent to 1-800-GET-THIN and eight other affiliated surgery centers — give the outfits 15 days to figure out how to correct their misleading ads. The agency’s move comes in response to complaints from Los Angeles County’s public health agency and even from Allergan, which manufactures the Lap-Band device used in the gastric banding surgery, saying the risks of the surgery are not properly communicated.

MORE: Why Some Weight-Loss Surgeries Increase Alcohol Risk

The use of smiling, thin people and seductive ad copy like “Lose weight with the Lap-Band! Safe 1 Hour, FDA approved” preys on the ads’ target audience. “They’re speaking to a very vulnerable patient population,” Steve Silverman, an FDA director who oversaw the investigation that led to the warning letters, told the Los Angeles Times. “People who are obese have often struggled through their whole lives to lose weight.”

Five patients in southern California have died since 2009 after undergoing weight loss surgery at centers affiliated with 1-800-GET-THIN, the Times reports.

Lap-Band surgery (or laparoscopic adjustable gastric banding surgery) involves placing an inflatable band around the upper stomach in order to limit the amount of food the stomach can hold. It is a popular alternative to gastric bypass surgery, which involves stapling off a section of the stomach and rerouting food to bypass the small intestine. Recent studies have shown that Lap-Band patients suffer a high rate of complications, however, both major and minor: in March, a study found that 40% of patients experienced serious complications following surgery and an additional 22% had minor complications; 60% needed subsequent surgery.

MORE: Study of Weight-Loss Surgery Complications Revives a Question: Bypass or Banding?

In addition to concerns over patient safety, the Lap-Band industry in California is under scrutiny for business practices. Reported the Times:

In California, Insurance Commissioner Dave Jones also is investigating the Lap-Band industry over questions about alleged fraudulent billings and misrepresented charges. He did not single out the surgical centers named by the FDA but said his office is generally aware of complaints about deceptive advertising. “We are continuing to look at the operations of these facilities,” Jones said. The patients’ deaths and injuries have also prompted a series of wrongful-death and personal injury lawsuits against 1-800-GET-THIN, its affiliated surgery centers and doctors who performed the procedures. There’s also a class-action lawsuit, filed on behalf of patients, that accuses 1-800-GET-THIN of false advertising for failing to adequately disclose risks of the surgery and disciplinary problems of some affiliated doctors.

For more, you can see the FDA’s full warning letter here.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.