Legal Question in Employment Law in California

Theoretically, yes, but there would be no sense in doing anything other than making it anything BUT pre-tax whenever allowed. Benefits treated as pre-tax are not subject to payroll taxes for the employee or employer, except medicare tax. They are deductible business expenses for the employer either way. But if the employer stupidly deducts them from taxable payroll, instead of before they are subject to payroll tax, the employer screws not only the employee - who has to pay income taxes on them - but the employer too, because the employer has to pay the employer's payroll taxes on them.