Specifically, the suit points out the similarities in the shape of the body, the wraparound windscreen and the easy-access mid-entry door.
Nikola filed for its patents in December 2015 and announced in May 2016 that it was designing and meant to build an electric Class 8 truck. Seventy-two days after the Nikola truck design was released, Musk announced that Tesla was in the "early stages" of developing a semi.
The company also claims a recruiter at Tesla tried to poach Nikola engineers shortly after its hydrogen truck was unveiled.
The hydrogen fuel-cell vehicle startup filed design patents on its Class 8 truck in December 2015 and showed off a real-world prototype in December 2016 (you can read Ars' coverage of that announcement here).
Nikola Corporation filed the lawsuit against Tesla Tuesday, May 1 in an Arizona-based U.S. District Court.
By Aug. 31, 2016, Nikola had 300 orders for more than 7,000 of its trucks with a total value of more than $2.3 billion.
In April 2017, Tesla released a teaser image of its semi, but the following November Nikola sent a letter to the company demanding that it not unveil its truck until a determination on whether it infringed on Nikola's copyrights were resolved, the suit says. "Upon information and belief, Tesla's market value jumped by roughly $2 billion after the Semi unveiling", the complaint notes.
A prototype version of the Semi was revealed during Tesla's own, splashy event last November, Musk teasing the event by promising attendees should prepare to have their minds blown "clear out of your skull and into an alternate dimension".
Nikola has sparred with Tesla before, including how it chose to use the first name of the same famous investor when founding the company. "Further, any problems with the Tesla Semi will be attributed to the Nikola One, causing harm to the Nikola brand". The facility where it will manufacture the trucks does not yet exist, and apparently, neither does the money for it.
In January of this year, Nikola announced plans to build a 1 million square-foot plant in Phoenix to produce both the Nikola One and smaller Nikola Two models, with the facility expected to be completed in 2024.
Nikola's attorneys did not immediately respond to a request for comment; and a spokesperson for the company declined to comment.