South Korean girl group Oh My Girl has been detained at a U.S. airport for 15 hours after its members were mistaken as sex workers, the group’s agency said Friday.

The eight-member act had no issue passing through immigration at the Los Angeles International Airport on Wednesday, but problems emerged when customs authorities started questioning the relationship between its members and the agency staff, WM Entertainment said.

One of the staff members mistakenly used the word “sister” to describe the relationship, and U.S. authorities seem to have taken the members as sex workers after examining their costumes and props, it added.

The group had arrived there for a photo shoot for their next album cover. They were also to promote themselves at the Unforgettable Gala of 2015, an event gathering Asian-American entertainers and producers in L.A. on Saturday.

After having their cell phones confiscated, however, the staff decided to fly the members back to South Korea, where they arrived earlier Friday.

WM Entertainment said no entertainer’s visa was necessary for the group to attend the event since it wasn’t a solo concert.

It also said it has hired a U.S. attorney to investigate whether the detention was unlawful.