U.S. automakers General Motors (GM) and Nikola (NKLA) have not finalized an agreement to jointly manufacture electric pickup trucks and hydrogen fuel cell tractor-trailers but will continue negotiations on the matter, a GM spokesperson said Tuesday.

"Our transaction with Nikola has not closed," GM spokeswoman Juli Huston-Rough said. "We are continuing our discussions with Nikola and will provide further updates when appropriate or required."

On Sept. 8, GM announced a $2 billion partnership with Nikola on electric pickup trucks. Yet, several controversies have complicated discussions on the deal.

On Sept. 10, Hindenburg Research released a report accusing Nikola founder and executive chairman Trevor Milton of lying about his company’s technology in order to form partnerships with major automobile companies. Milton has also been accused by several women of sexual assault.

Milton, 38, resigned from his executive chairman position on Sept. 20. The Department of Justice and Securities and Exchange Commission are investigating Milton and Nikola over fraud allegations.

Milton founded Nikola in 2014, with the company based in Phoenix. The firm specializes in vehicles using hydrogen fuel cell technology.

One of Nikola’s main competitors is electric vehicle giant Tesla Inc. (TSLA). Tesla CEO and founder Elon Musk has called hydrogen fuel cell technology "mind-bogglingly stupid."