As a result, the law only provides subsidized coverage on the new insurance marketplaces to people with incomes between 100 and 399 percent of the poverty level, excluding people below that line.
Those individuals would otherwise be covered by Medicaid, but the Supreme Court decision upholding the Affordable Care Act made the expansion optional for states.
Twenty-six states have decided either not to expand their programs or are undecided, meaning many below the poverty line will not benefit from ObamaCare's new coverage options, said Commonwealth, a nonprofit research foundation.
The healthcare law's stated mission is to expand health insurance to as many people as possible, and this unforeseen gap in government help for some below the poverty line runs against that goal.
While some states are expected to back the Medicaid expansion later on, study authors urged Congress to pass a bill allowing people below the poverty line who are not eligible for Medicaid to gain subsidized coverage on the new insurance exchanges.
"This would ensure that all Americans have access to the law's sweeping new reforms when they take effect in January," the report stated.
Twenty-one states plus the District of Columbia are expanding their Medicaid programs. Three other states are expanding their programs in a non-traditional way.