SolarCity, the solar energy company Tesla acquired last year, has fired hundreds of additional workers, according to six anonymous sources who talked to CNBC. These dismissals are in addition to hundreds more that were reported earlier this month, and they are on top of previously announced layoffs, CNBC reports. All told, around 1,200 people at Tesla and SolarCity have lost their jobs in the recent wave of firings, employees told CNBC.

Reached by e-mail, Tesla referred back to a statement sent out earlier this month when the initial firings were announced. "As with any company, especially one of over 33,000 employees, performance reviews occasionally result in employee departures," the company wrote in early October. The company says that recent departures were part of the same review process. The company also emphasized that the process also led to "recognition of top performers with additional compensation and equity awards."

Some employees weren't happy with how the process was carried out. SolarCity employees told CNBC that they "were surprised to be told they were fired for performance reasons, claiming Tesla had not conducted performance reviews since acquiring the solar energy business."

CNBC says some employees were fired individually, while others were fired in group meetings. Three employees told CNBC that they asked for copies of their negative performance reviews but hadn't gotten them. A Tesla spokesperson declined to comment on how the review process was conducted.

In September, SolarCity announced around 200 layoffs in offices in Roseville, California. Those notifications were required by California's WARN Act, which requires advanced notice if companies lay off more than 50 people. But the new round of job losses extends well beyond that office, employees said, with firings in Nevada, Arizona, Utah, and elsewhere.

SolarCity signaled in May that it was ending door-to-door sales. The company said at the time that affected employees would be considered for other jobs within the company.