Mr. Diaz, like Tesla itself, likened the plant to a small city — one in which experiences can vary, he said. “You know, you can have something that happens in one part of the city that doesn’t happen in another part,” he said. But when his son encountered racial slurs and caricatures in a different part of the factory, Mr. Diaz concluded that the issue was not an isolated one.

One suit accusing Tesla of racial discrimination and harassment, filed last November in California Superior Court, seeks class-action status. The lawyers involved — Lawrence A. Organ and Bryan Schwartz, whose practices focus on workplace rights — say they have identified dozens of potential plaintiffs. Each lawyer has won multimillion-dollar judgments in other harassment or discrimination cases against major employers. Tesla is seeking to move the case into arbitration, which would require workers to bring individual lawsuits rather than a joint claim.

The state’s Department of Fair Employment and Housing says it has issued 10 “right to sue” letters — a precondition for a discrimination lawsuit — to employees complaining of racial bias at the Fremont plant. Dozens of other complaints against Tesla are pending, but the agency would not say how many involved race.

In an email to employees last year, which the company later released in response to one of the lawsuits, Elon Musk, Tesla’s chief executive, warned against “being a huge jerk” to members of “a historically less represented group.” At the same time, he wrote, “if someone is a jerk to you, but sincerely apologizes, it is important to be thick-skinned and accept that apology.”

But by many accounts, the issues at the Tesla factory go beyond the need for a thick skin.

High Hopes

When employees and contractors are counted together, there are more than 15,000 workers at the Fremont factory, but it is not clear how many are African-Americans. The company says more than two-thirds of the production leads — those directing work in different areas of the factory — are nonwhite. But it would not specify the share of jobs held by African-Americans, who have long been underrepresented in other Silicon Valley workplaces.

In any case, some African-American workers who expected to help build a future for the company and themselves, like Teshawna Stewart, say the reality proved to be a slap in the face.