None of the new distortions that the Senate health-care bill will layer onto the already-distorted tax code have received the attention they deserve, but in particular its effects on marginal tax rates could use scrutiny. Incredibly, for those with lower incomes, ObamaCare will impose a penalty as high as 34% on . . . work.

Central to Max Baucus's plan—assuming the public option stays dead—is an insurance "exchange," through which individuals and families could choose from a menu of standardized policies offered at heavily subsidized rates, provided that their employers do not offer coverage. The subsidies are distributed on a sliding scale based on income, and according to the Congressional Budget Office 23 million people will participate a decade from now, at a cost to taxpayers of some $461 billion.

Think about a family of four earning $42,000 in 2016, which is between 150% and 200% of the federal poverty level. CBO says a mid-level "silver" plan will cost about $14,700 in premiums, of which the family will pay $2,600—since the government would pay the other $12,100. If the family breadwinner (or breadwinners, because the subsidies are based on combined gross income) then gets a raise or works overtime and wages rise to $54,000, the subsidy drops to $9,900. That amounts to an implicit 34% tax on each additional dollar of income. [...]

The incentives for low-wage workers are especially perverse. The exchanges give them a huge break and then take it away gradually as their income goes up. Usually such phase-outs are used to make sure "the rich" don't benefit from IRS dispensations, but here they will have a giant effect on decisions about whether and how much to work, since each additional hour worked reduces the subsidy.