If you receive both Social Security Disability and Workers Compensation Benefits: Social Security Benefits are taxable to a certain extent.
If you receive both Social Security Disability Benefits and Workers Compensation, then Social Security may be reduced by a certain amount due to your receipt of Workers Compensation Benefits (you can only receive up to 80% of your pre-disability earnings form both sources, otherwise, Social Security reduces its benefits).
The IRS tax you on the FULL amount of the Social Security Benefit, even if it has been reduced by Workers Compensation.