As 2014 approaches, the new health insurance exchanges will begin their open enrollment, and along with the new exchanges will come the premium assistance tax credit, intended to make health insurance purchased on an exchange more affordable for the "lower income" - which is actually broadly defined to include everyone up to 400% of the Federal Poverty Level. As income rises, the premium assistance tax credit is slowly phased out, until eventually it provides no benefit at all.
However, the reality is that because the premium assistance tax credit phases out as income rises, it indirectly serves as a surtax that triggers higher marginal tax rates for those who are phasing the credit out. And the marginal impact is actually quite significant; at relatively modest levels of gross income from $25,000 to $50,000 of income, the premium assistance tax credit effectively doubles the marginal tax rate (to more than 30%) for those who are purchasing health insurance from the individual exchange. For older households that are claiming Social Security early, but still obtaining health insurance from an exchange (as they're not eligible for Medicare yet), the effect can be even more severe, as marginal tax brackets, the phaseout of the premium assistance tax credit, and the phasein of Social Security taxability all overlap.
The end result doesn't mean that it's a good idea to avoid generating income - the marginal tax rates are significantly higher than just the individual's tax bracket, but nowhere near 100% tax rates. Nonetheless, the introduction of the premium assistance tax credit may mean a whole new level of in-depth year-to-year tax planning for those with relatively modest incomes, who can be subject to surprisingly high marginal tax rates under the new rules.