He says his amendment would ensure these immigrants do not receive preferential treatment above those who came here legally.
"This is only fair," said Hatch, a coveted swing vote on the bill. "After all, even those who were U.S. citizens at the time the health law was passed have had to wait nearly five years for the law to go into effect so they could access these credits and subsidies."
The federal health law is still loathed by most conservatives and looked at skeptically by much of the public. Republicans plan to use it as a weapon against Democrats in the 2014 midterm elections, when new health-insurance exchanges are rolled out in each state, and health care has become a touchy issue in the immigration debate.
Rep. Raul Labrador, R-Idaho, walked away from House negotiations because he couldn't support health care provisions for unauthorized immigrants. The bipartisan bill negotiated in the House has yet to be publicly released.
The Senate bill already says undocumented immigrants seeking legal status cannot obtain any premium credits or subsidies until they gain a green card, a path that would take at least 10 years.
Hatch's amendment would extend that for another five years after they gain a green card. Immigrants with green cards can obtain citizenship in three years, meaning that under the Hatch plan a number of these people would be American citizens before they could access federal health subsidies. That's in line with prohibitions on access to Medicaid and other federal programs.
Hatch called it an "oversight" that negotiators failed to extend this same policy to Obamacare.
"I simply want to ensure," Hatch said, "that we're not creating a new class of people with special access to federal benefits."
Democrats bristle at his amendment, even as they consider whether accepting it is worth gaining Hatch's support.
They note that legal permanent residents can access Obamacare subsidies without a waiting period and they question why the same standard shouldn't apply to undocumented immigrants who eventually obtain a green card.
"There is no reason to change that for one group of legal permanent residents because of how they got there," Cecilia Muñoz, director of the White House's Domestic Policy Council, told a group of newspaper reporters recently.
Sen. Mazie Hirono, D-Hawaii, said she, like Hatch, wants no better or worse treatment for these immigrants, but added that they are already at a disadvantage in the bill.
They have to pay taxes for at least 13 years before gaining full access to federal benefits.
"We are saying to these immigrants, 'Pay your taxes but if your kids get sick don't come to us for help,' " she said. "We are saying, 'Pay your taxes but if you have to work part time because of a recession, don't come to us if you need some help putting food on the table.' We are saying, 'Pay your taxes, but we're not going to help you.' That is just not fair."