In a recent IRS FAQ, the IRS reiterated that arrangements in which an employer reimburses its employees' for the cost of individual (i.e. not 'group') health plans on a pre-tax basis is prohibited.
In the past, employers have been permitted to reimbursed an employee for the cost of health insurance policy premiums (or pay those premiums directly) and exclude those payments from the employee's gross wages. Such an arrangement is called an "Employer Payment Plan", and as a result of the Affordable Care Act (ACA), are now considered to be "group health plans subject to the market reforms, including the prohibition on annual limits for essential health benefits and the requirement to provide certain preventive care without cost sharing." Employer Payment Plans cannot be integrated with individual policies in order to satisfy these market reforms, and therefore may be subject to a $100/day excise tax, per employee!
The bottom line is that employer reimbursements (or direct payments to the insurer) for the cost of an employee's individual health insurance policy can no longer be made on a pre-tax basis. This does not prohibit the employer from making those same payments on an after-tax basis.