There is no doubt that this pinched approach will put a significant number of workers and their dependents in a bind. A Kaiser Family Foundation survey found that in 2012, employees’ annual share of insurance premiums averaged $951 for individual coverage and $4,316 for family coverage. Under the I.R.S. rule, such costs would be considered affordable for an employee with a household income of $35,000 a year — making the employee’s spouse and children ineligible for a public subsidy on a health exchange, even though that family would have to spend 12 percent of its income for the employer’s family plan.

Estimates made in 2011 by respected research organizations suggested that some 2 million to 3.9 million non-working spouses and dependents would be harmed by the strict ruling. Looking only at children who were uninsured but supposed to gain coverage under health care reform, the Government Accountability Office estimated last June that 460,000 might remain uninsured because of the affordability definition, and that 1.9 million might stay uninsured if an existing children’s health insurance program is phased out as currently planned. This outcome is exactly the opposite of what health care reform is supposed to achieve.

It is hard to see what might be done to reverse this deplorable result. The ideal solution would be for Congress to clarify that the 9.5 percent calculation is based on a family plan, and that dependents can get subsidies on the exchanges if there is no affordable coverage at work. But House Republicans, who are bent on obstructing the health reform law, would never agree to helpful changes, especially one that would increase federal spending.

This problem increases the need to retain the children’s health insurance program, which is financed only through 2015. And it will be crucial to assess the impact that this misguided provision has on coverage, access to care, and the financial burdens on families of modest means.