Disability pay is taxable if the disability policy was paid for by your employer as an employee benefit. You are having taxes withheld as if it was a paycheck for working, and you should expect to get a W-2 at the end of the year and file a tax return reporting this as taxable income as if it was from working.
If you had a private disability policy that you paid for out-of-pocket (after tax, not as a pre-tax payroll deduction) then it should not be taxable and you should contact the insurance company.
