The IRS has provided for a safe harbor for businesses at risk of failing to provide for health insurance for “all” of their full-time employees under the Affordable Care Act. According to proposed regulations,

After further study and consideration of the comments, the Treasury Department and the IRS believe that they should exercise their administrative authority to allow recognition of a margin of error consistent with an intent to recognize the possibility of inadvertent errors together with the specificity and administrability of a specific percentage, and therefore have concluded that a clear and definitive 95 percent standard would be an administrable and appropriate interpretation of the statutory provision.

The proposed regulation is here.