Arizona officials called attention to the problem last week, when Republican Gov. Jan Brewer opted to accept the Medicaid expansion.
Brewer had been a leading opponent of the overhaul, and her decision got widespread attention. State budget documents cited the immigration glitch as one of her reasons.
"If Arizona does not expand, for poor Arizonans below [the federal poverty line], only legal immigrants, but not citizens, would be eligible for subsidies," the documents said.
That's because the immigrants would be eligible for government-subsidized private insurance, while low-income citizens would not. The Obama administration confirmed Arizona's interpretation.
The gist of what Brewer was saying is that "by rejecting the expansion, you are essentially rewarding the immigrant population at the expense of full citizens," said Matt Salo, executive director of the National Association of Medicaid Directors, a nonpartisan group that represents the states in Washington.
"The political optics of that could be crushing."
It could take some explaining for Texas Gov. Rick Perry, steadfastly opposed to what foes dismiss as "Obamacare," and for Florida Gov. Rick Scott, who is reassessing his position. Both states have large numbers of uninsured citizens and legal immigrants.
"I think politicians will be under a lot of pressure not to create these sorts of inequities," said Jennifer Ng'andu, a health policy expert with the National Council of La Raza, one of the major Latino advocacy groups. Her group supports the health-care law and is urging every state to accept the Medicaid expansion.
The quirk in the Affordable Care Act was not planned, but came about on the twisting route laws take from Congress to the president's desk to the courts.
To be sure, no one is talking about the government buying health insurance for illegal immigrants. That's not allowed under Medicaid or Obama's law. Instead, the issue is between U.S. citizens and legal immigrants, those who are lawfully in the country.
So far, 11 states have said they're not interested in the Medicaid expansion, while 17 states and Washington say they are taking it. The rest are weighing their options. The immigration glitch is a consideration.