Amazon.com on Thursday unveiled plans to retrain a third of its U.S. workforce — or 100,000 workers — by 2025 to help its employees move into more advanced jobs or find new careers.

The retail and tech giant intends to expand its existing training programs and introduce new ones. The training will be voluntary, and most of the programs are free.

Programs will help workers "access training to move into highly skilled technical and non- technical roles across the company's corporate offices, tech hubs, fulfillment centers, retail stores, and transportation network, or pursue career paths outside of Amazon," the company said in a statement.

Amazon's retraining programs will include:

Amazon Technical Academy, which equips non-technical employees with the skills to transition into software engineering careers;

Associate2Tech, which trains fulfillment center associates to move into technical roles;

Machine Learning University, which offers employees with tech backgrounds the opportunity to access machine learning skills;

Amazon Career Choice, a pre-paid tuition program designed to train fulfillment center associates in high-demand occupations of their choice;

Amazon Apprenticeship, a Department of Labor certified program that offers paid intensive classroom training and on-the-job apprenticeships with Amazon; and

AWS Training and Certification, which provide employees with courses to build practical AWS Cloud knowledge.

The planned program is among the biggest corporate retraining initiatives ever announced, at a cost of roughly $7,000 per worker, or $700 million.

Amazon and other companies have struggled to find technically qualified U.S. employees. More advanced training for workers hired to work in Amazon warehouses is occurring in an increasingly competitive environment with the unemployment rate hovering below 4%.

Major retailers like Walmart and Target have been raising pay and boosting training to lure more quality employees and to make the experience in stores less stressful.