Disability insurance pays wage replacement benefits to employees who are not working because of non-job-related accidents or illnesses. (Workers' compensation covers job-related injuries.) It also provides coverage for employees who may not be eligible for workers' compensation, or it may supplement workers' compensation.
A few states have laws that require employers to provide disability insurance, but Washington is not among them. Washington employers may provide such insurance, but they are not required to do so. State law may require specific provisions in a group disability policy sold by insurers in Washington.