see this link
https://accountinginsights.org/why-is-my-dp-imputed-income-taxed-1000-per-month/
likely the fair value of the benefits (because the employer may be picking up a portion) is greater than the actual payroll deduction.
we have no access to the employer's records so have no way of knowing if the calculation is correct.
from the article
Employers should (no requirement that i know of in the tax laws) explain how the imputed amount is calculated. if it refuses, the IRS is not going to get involved so you would probably need a lawyer.
