Taxation of Domestic Partner health coverage where DP is one of several dependents

[Guest Amanda Davis]

We are planning to implement domestic partner coverage effective 1/1/04. Currently, our premium structure is just 2 tier--single and family.

If an employee who already has elected family coverage for covered dependent children elects to add his/her DP, can we tax the entire portion of premium attributable to family coverage?

Or, must we tax some determined amount of the family portion that may be attributable to the DP portion of coverage? Again--we only have 2 tiers. How would we determine what the portion of premium is attributable to the DP and which portion is attributable to the dependent children?