Nikola (NKLA 0.11%) stock was falling by double digits Thursday morning. After plunging as much as 16%, shares of the electric heavy truck maker were still down by 10% as of 10:35 a.m. ET.

The drop came after the company chairman filed a proxy statement including a letter to stockholders that highlighted a contentious battle for seats on the company's board of directors. It also follows a recent analyst report that noted several hurdles that could impact Nikola's successful growth.

A former chairman is still a thorn

The chairman's letter reviewed much of the progress the electric truck maker has made with its battery- and hydrogen-fueled electric trucks. But chairman Steven Shindler also used a meaningful portion of his letter to discuss a battle for board seats. Shindler pushed back on founder and former chairman Trevor Milton's attempt to regain decision-making abilities at the company. He noted that "M&M Residual, LLC, an entity controlled by criminally convicted former Executive Chairman Trevor Milton, has provided notice of its intent to nominate a slate of Directors."

Shindler warned investors that Nikola does not endorse the M&M Residual nominees. He said they lack public company experience, as well as expertise and knowledge of the business.

Knowledge and expertise will be necessary as the company works to build out infrastructure for its hydrogen fuel cell trucks. That step in its path to success was also noted as a critical hurdle in a report from Wolfe Research analyst Scott Group earlier this week. Group noted sparse charging infrastructure and hydrogen fuel costs as barriers to customer engagement with the new heavy truck technology.

With the stock having run 30% higher over the last month, some investors are taking profits amid these concerns. There's no doubt Nikola is a highly speculative stock. It will need to get past Milton's attempts to regain a say in the business as it works to focus on building out that needed hydrogen infrastructure and gain sales momentum.