Senate Republican staffers estimated Thursday that the annual cost to taxpayers of legalizing illegal immigrants could be in the billions, if they use their status to apply for federal benefits from Medicaid and ObamaCare. The claim, though, was challenged by Florida Sen. Marco Rubio, a key Republican engaged in immigration bill talks.

Republicans on the Senate Budget Committee — responding to an emerging immigration proposal that includes a path to citizenship for millions of illegal immigrants — had estimated that the cost could total up to $40 billion in 2022, “just for Medicaid and ObamaCare.”

“The net costs would be enormous and only increase once citizenship is granted,” the office of Alabama Sen. Jeff Sessions, top Republican on the committee, said in a statement Thursday. The estimates were crunched by budget committee Republican staff.