The IRS recently put out a reminder in the form of an FAQ regarding employer payment plans. Generally, arrangements funded on a pre-tax basis that reimburse employees who purchase individual health policies are considered group health plans. This means that they must comply with the ACA market reforms, such as the prohibition on annual limits. These arrangements cannot be integrated with individual policies to satisfy the market reforms, which typically results in noncompliance.
IRS Notice 2013-54 has more information and includes guidance on the use of HRAs and FSAs to reimburse premium expenses.