Clement argued that Medicaid was established in 1965 as a cooperative federal-state partnership, but the new law creates a "massive expansion" of that relationship.
Beginning in 2014, states will be asked to cover all individuals younger than 65 with incomes up to 133 percent of the poverty level. Although the federal government will initially fund 100 percent of that expansion, by 2017 states will be responsible for 5 percent of those costs, with that number increasing to 10 percent by the end of the decade.
Immediately, Justice Elena Kagan challenged Clement's argument that the federal government was coercing states to participate.
"Why is a big gift from the federal government a matter of coercion?" she asked. She referred the money given to the states as a "boatload of federal money."
Clement said that Congress made the new terms a condition of continued participation in Medicaid.
Although the justices have finished hearing arguments, in many ways their real work now begins.
They will meet behind closed doors to discuss the arguments.
The justice who is most senior on the majority side will assign writing the opinion.
Drafts will begin to circulate among the chambers and a decision is expected by late June.