By: CHRIS ISIDORE, CNN BUSINESS

(CNN) – Layoffs for about 4,000 salaried staff at General Motors are due to start Monday.

The layoffs are part of a 15 percent reduction in white collar jobs in North America that the automaker first announced back in November. At the same time, it announced plans to close four US plants as well as a fifth in Canada.

While those plants, which include about 6,000 hourly jobs, have yet to close, GM is moving ahead with the salaried staff reductions, a GM spokesman confirmed Friday. The timing of the layoffs was first reported by the Detroit News.

The company had about 2,300 salaried staff accept voluntary buyout packages that were offered to 18,000 employees. In addition, there were 1,500 contract employees who were not retained by the company.

That leaves the remainder of the 8,000 planned job cuts to be accomplished with the involuntary layoffs.

GM is due to report financial results Wednesday and it is expected to report lower earnings.

The job cuts and plant closings are part of ongoing cost reductions to free up $6 billion annually to invest in a new generation of autos, such as electric and self-driving vehicles. It is also making a push to develop a ride hailing service that will allow GM to make more money by selling rides to customers rather than vehicles.