Shares of Nikola Corp. (NKLA) sank more than 9% in early tradin🐻g on Monday after the electric vehicle (EV) maker voluntarily recalled 209 of its Class 8 Tre semi-trucks because of potential battery fires. The company said it is also putting a hold on sales of any new battery electric vehicles (BEV) until a resolution is in place.

Nikola said that internal and third-party investigations found that a coolant leak inside a battery pack was the probable cause of a June 23 fire in a truck at the firm’s headquarters in Phoenix. The problem was corroborated on Aug. 10, when an engineering validation truck at the company’s Coolidge, Arizona, plant had “a minor thermal incident” affecting a battery pack. No injuries were reported in either incident. 

The EV maker said that a single supplier component within the battery pack was the likely source of the leak. It added that “efforts are underway to provide a field remedy in the coming weeks.” In the meantime, BEV truck owners and de𓄧alers are being advised to take steps to help the company monitor the vehicles.

Nikola noted that its hydrogen fuel cell EVs currently in production aren't affected because their battery packs have a different design.

Nikola shares fell to their lowest level in more than a month following the news.