As Capretta explains as a family moves from the lowest category to the next ( slight higher) run of the economic income ladder they loose a major portion of the government subsidy which is offered to help pay for the the health insurance the government is forcing them to buy.Here is a quote from that article detailed what is in effect an "implicit marginal tax" of no small proportion:
"According to CBO, family coverage in 2016 is likely to cost about $14,400 under the so-called “silver option” in the health-care reform plan sponsored by Senate Finance Committee Chairman Max Baucus. In the Baucus plan, a family of four at the poverty line (about $24,000 in 2016) would have pay to about $1,400 toward coverage, with the federal government paying the other $13,000 on their behalf. In addition, the government would also provide $3,500 to reduce the family’s deductible and co-payment costs for health services. Thus, the new entitlement provided by the Baucus bill would be worth a whopping $16,500 for a family at the poverty line.
As incomes rise, however, the Baucus bill cuts the value of the entitlement. A family with an income at twice the poverty line, or $48,000 in 2016, would get $9,072 in federal assistance for coverage — still a substantial sum. But it’s $7,400 less than the family would get if they earned half as much. The Baucus plan thus imposes an implicit marginal tax rate of about 30 percent ($7,400/$24,000) on wages earned by families in this income range."