US musician Andra Day and Hyundai Motor Co. were accused of falsely hiring unpaid South Korean volunteer musicians in what was known to be the singer's new music video shoot but was actually part of a promotion project for Hyundai, according to participants Thursday.

Rockin' 1000, an Italy-based music event group, partnered with ad agency Innocean Worldwide Americas in recruiting volunteer musicians -- singers, guitarists, bass player and drummers -- to be part of "a new music video" for Day's song "Rise Up."

The music video was planned as a promotional tie-in project for Hyundai's new G70 sedan, which launches Sept. 15. Filming took place from Aug. 25-27 in Seoul and Gyeonggi Province near the capital.

The problem is that Rockin' 1000, responsible for recruiting the South Korean volunteers, was not crystal clear about the exact nature of the project. The organization announced that the project was aimed at filming a new music video for "Rise Up" and left out any details of its affiliation with Hyundai.

Many volunteers, mostly amateur musicians, vented frustration over the Internet after learning that they were mobilized in a commercial project for a third party.

"Initially we were told that the project was to film a 'remastered' version of Andra Day's 'Rise Up' music video. But on the second day of the shoot, suddenly a gray Hyundai sedan showed up as a prop," 22-year-old participant Kim Jong-min, who majored in guitar at college, told Yonhap News Agency.

According to Kim and others, many volunteers protested after learning late into the first day of filming that they were actually in a promotional project for Hyundai's G70. Yonhap News obtained a copy of a non-disclosure agreement that the volunteers had signed on the day of the shoot. Hyundai was mentioned in the document.

"We asked each other, 'What is this?' and suddenly one volunteer just left in protest," Kim said. He said many from the approximately 100 volunteers left the project by the final day of the shoot.

Park Dong-min, another participant, confirmed Kim's account. He recalled being told from organizers that "The footage will not be used as a commercial." But behind the scenes snippets from the shoots were available for viewing on Hyundai's Instagram account (https://www.instagram.com/genesisworldwide/).

"I'm trying to force myself to justify that it was a good memory to look back upon," Park told Yonhap News over Facebook chat.

Kim recalled a senior member from Rockin' 1000 tried appeasing the volunteers who became uncomfortable with the situation.

"He said through an interpreter, 'This is not a commercial but a pure music video.' He said the production needed money, hence agreed to a tie-in with the automaker."

Mule, a South Korean online music community, was also filled with claims of volunteers being duped by the organizer over the exact nature of the project. Many have called for Hyundai to pay for their appearance in its commercial project.

Warner Music Korea, the South Korean branch of Day's label Warner Music Group, said it had no information whatsoever regarding the project. The singer is scheduled to appear at Hyundai's G70 launching event in Seoul on Sept. 15.

"We've not been told anything from Hyundai. It would be appropriate for them to contact us, but we're not aware of the exact circumstances," said a spokeswoman at Warner Music Korea, adding that she learned of the project belatedly over social media.

Volunteers claimed the singer was apparently aware of the project's nature. They said the songstress drove inside a G70 during the shoot. She was filmed for about two hours, according to witnesses.