The ACA can tax the same dollar of labor income 4 times, with each instance coming from a different part of the statute.
In counting 4 tax instances, I am not counting normal federal income tax, state income tax, the earned income tax credits, sales taxes, excise taxes, etc. — just stuff in the ACA itself. Nor I am counting the ACA’s new Medicare taxes, reinsurance taxes, medical device taxes, tanning taxes, brand name drug taxes, or any of the new taxes and credits associated with small businesses.
For now, I will give readers only a hint: when it determined that the ACA would increase marginal labor income tax rates by 20+% for some taxpayers, the Congressional Budget Office was considering only one of the four instances. As far as I know, none of the CBO’s publications acknowledge or examine the other three provisions as implicit taxes on labor income. Nor has the CBO necessarily identified the single largest (in marginal tax rate terms) of the four provisions, even though 20+% by itself is admittedly large.