Apple has revealed it will lay off 139 employees located in both Sunnyvale and Santa Clara offices, who work within its autonomous vehicle department, Project Titan. Apple announced the planned layoffs and included details in a letter to the California Employment Development Department, stating the employees will be let go effective April 16.

The Apple employees being laid off consist of 38 engineering program managers, 33 hardware engineers, 31 product design engineers and 22 software engineers, all of whom had been developing the company’s extremely secretive self-driving cars.

Speculation about the layoffs has brought up Apple’s struggling iPhone sales, which have continued to decrease. The tech giant has seen a 15 per cent drop in revenue over the last three months, which could be partially due to China’s ongoing economic slowdown. This is not the first instance of Apple laying off Project Titan employees. The company has downsized its self-driving car unit by hundreds of employees since 2016.