A New York City couple pleaded guilty to charges of illegally injecting women in Honolulu with wrinkle-reducing drugs similar to Botox and attempting to smuggle to South Korea nearly $80,000 cash hidden in sanitary napkin containers, federal prosecutors said.

Bu Young Kim and her husband Chan Hui Cho, of Whitestone, New York, imported the drug Dysport from South Korea, according to court documents. Kim is also known as "Pretty Sister," a document states.

The couple would fly to Honolulu where Kim injected women — mostly from the Korean community — with the drug in places such as rooms at Honolulu's Pagoda Hotel, Assistant U.S. Attorney Ken Sorensen said Friday.

The couple charged between $100 and $500 for the treatments but didn't tell customers that "Kim was administering and dispensing prescription drugs that only a licensed practitioner could administer and dispense," according to a court document.

On March 6, the couple tried to board a flight to South Korea from Honolulu International Airport, where they told customs officials that they were only carrying $9,000. Travelers carrying more than $10,000 cash must declare it. When agents searched their luggage, there was $79,986 hidden in packages of sanitary napkins, Sorensen said.

Honolulu attorney Michael Green, who along with a colleague represents the couple, said they didn't know they were doing anything illegal. There's high demand in Hawaii and elsewhere for "Botox parties," he said.

Most of the couple's customers were women who work in Honolulu's strip clubs and bars and wanted to get cosmetic procedures at a discount, Green said.

The investigation was prompted by someone who got an infection and wanted to "shake them down," Green said.

Kim and Cho face up to five years in prison and a $250,000 fine when they are sentenced July 13.