Employee dismissals at Tesla are continuing at its SolarCity subsidiary, according to six former and current employees, and are affecting SolarCity offices across the U.S.

Echoing reports from earlier this month, these SolarCity employees say 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. Earlier this month, Tesla began firing hundreds of employees after it announced a recall of 11,000 Model X SUVs.

All the people spoke under condition of anonymity, citing fears of retaliation from Tesla.

Tesla had already announced plans to lay off 205 SolarCity employees at its Roseville, California, office by the end of October this year. However, SolarCity employees across the country have been fired in the last two weeks — not just in California, but also in Nevada, Arizona, Utah and beyond, according to these employees.

Two former employees told CNBC that the Roseville office was being completely shut down. A Tesla spokesperson said the office will remain open with about 50 full-time employees. In March 2015, SolarCity said it employed 450 people at that location and was planning to add 300 more. It is not known whether those new people were ever added.

The total number of dismissals could not be determined. However, former employees estimate around 1,200 people have been fired in the company's wave of dismissals at Tesla including SolarCity. That figure does not include previously announced layoffs.

A spokesperson for Tesla declined to confirm that number or offer an alternative, and pointed back to a previous statement about the companywide dismissals:

"Like all companies, Tesla conducts an annual performance review during which a manager and employee discuss the results that were achieved, as well as how those results were achieved, during the performance period. This includes both constructive feedback and recognition of top performers with additional compensation and equity awards, as well as promotions in many cases. As with any company, especially one of over 33,000 employees, performance reviews also occasionally result in employee departures. Tesla is continuing to grow and hire new employees around the world."

SolarCity, which sells solar energy systems to consumers, was founded by Elon Musk's cousins Lyndon and Peter Rive in 2006. Musk was its chairman and largest shareholder from its early days. When Must first proposed that Tesla buy SolarCity in 2016, critics said it would distract Tesla from making great cars.

Critics also raised corporate governance concerns because of the close relationships between the companies. Now, it operates as a subsidiary of Tesla.