Can an injured worker sue an employer for an on the job injury?
Yes. If the employer does not have worker's compensation insurance then the employer is a "nonsubscriber" and the injured employee may bring an ordinary negligence claim and recover monetary damages for pain and suffering, physical impairment, disfigurement, loss of wage earning capacity, and medical expenses.
Furthermore, a negligent employer that does not maintain worker's compensation insurance loses the right to reduce the injured worker's recovery by alleging that the accident was the result of the injured worker's own negligence unless the injured worker's negligence was the sole cause of the incident.
If an employer carries worker's compensation insurance the injured worker cannot sue the employer for an on the job injury.
There are two exceptions to the immunity granted by the worker's compensation law to negligent employers. An injured employee can sue an employer for an intentional injury and the dependent family members of a deceased employee can sue an employer to recover punitive damages if the employer's gross negligence causes the worker's death.