Nikola Corp. suspects “foul play” after an early-morning fire broke out at its Phoenix headquarters that affected several of its electric big rigs.

No one was injured in the blaze, the company said Friday in a tweet. An investigation is underway after a vehicle was seen in the area of the trucks prior to the incident, Nikola said.

More than 50 firefighters were dispatched around 4:30 a.m. local time to the scene, where they found four trucks on fire, Captain Todd Keller of the Phoenix Fire Department said in an interview. Investigators remain on scene but have not concluded whether the situation was a result of arson, he said.

Nikola didn’t comment beyond its tweet.

The situation adds to headaches for Nikola, which said last week it would cut 270 jobs to reduce expenses and preserve cash. It’s also grappling with delivery challenges, executive turnover and calls from its ousted founder, Trevor Milton, to replace leadership.

Shares of the company fell 6.5% to $1.28 as of 10:30 a.m. in New York.