A day after Lukasz Krupski put out a fire at a Tesla car delivery location in Norway, seriously burning his hands and preventing a disaster, he got an email from Elon Musk.

“Congratulations for saving the day!” Mr. Musk, Tesla’s chief executive, wrote in March 2019.

But what started as a story about a heroic employee and a grateful employer has devolved into an epic battle between the carmaker and Mr. Krupski, a service technician. The fight has spawned lawsuits in Norway and the United States and caught the attention of regulators in several countries.

After initially being hailed as a savior, Mr. Krupski said in an interview with The New York Times, he was harassed, threatened and eventually fired after complaining about what he considered grave safety problems at his workplace near Oslo. Mr. Krupski, originally from Poland, was part of a crew that helped prepare Teslas for buyers but became so frustrated with the company that last year he handed over reams of data from the carmaker’s computer system to Handelsblatt, a German business newspaper.

The data also provided the basis for stories by Handelsblatt and Wired magazine about how much trouble Tesla was having manufacturing the Cybertruck pickup, which the company has said will be delivered to customers at the end of this month, almost three years behind schedule. (Some of the information came from a second, unidentified Tesla employee.)

Mr. Krupski said he had gotten access to sensitive data simply by entering search terms in an internal company website, raising questions about how Tesla protected the privacy of thousands of employees and its own secrets.

The Data Protection Authority in the Netherlands, where Tesla has its European headquarters, is investigating whether the breach violated privacy laws. A spokeswoman for the authority confirmed that it was investigating but declined to comment further.

Tesla and three lawyers representing the company did not reply to requests for comment.

In the United States, Benson Pai, a former Tesla production worker, has sued the automaker in federal court in California, claiming that lax security by Tesla exposed employee information that could be sold to criminals. Lawyers for Mr. Pai are seeking approval from a judge to pursue the case as a class action on behalf of tens of thousands of Tesla employees.

Mr. Krupski shared the data with Aaron Greenspan, a prominent Tesla critic and short-seller, who urged him to provide information he had collected about Autopilot to the U.S. National Highway Traffic Safety Administration. The safety agency has had a long-running investigation into the software, which can steer, accelerate and stop a car on its own but requires a driver to be ready t