Yes, but that almost never happens. Are you sure?
The only case where this is routine is the case of domestic partner benefits. In that case, the employee's share of the premium should be deducted pre-tax but the DP's share of the premium must be deducted after-tax. In every other case I can think of, the employee's share should be deducted pre-tax. If the employer is truly deducting the employee's share after-tax, then the employer is harming not only the employees but themself (since deducting the premiums pre-tax reduces the employee and employer share of social security and medicare tax).
