A Vanderbilt University law professor's brief on the Affordable Care Act's Medicaid expansion provision helped shape the U.S. Supreme Court's recent ruling.

Vanderbilt Professor of Health Law and Policy and Constitutional Law James Blumstein submitted his brief to the Supreme Court, and it was cited by Chief Justice John Roberts in the court's decision that the ACA's Medicaid mandate could not be enforced.

The ACA's Medicaid expansion would have expanded coverage for all individuals with incomes under 133 percent of poverty, which would, according to a Vanderbilt release, significantly increase costs in coverage while simultaneously decreasing a state's flexibility in setting eligibility criteria for Medicaid.

Prior to the ruling, states would feel pressured to accept the Medicaid expansion mandate or face a loss in eligibility for the federal government matching 90 percent of state's Medicaid funding. With the ruling, states now can choose to participate in the Medicaid mandate, or without facing penalty, preserve their existing Medicaid programs.

Blumstein's brief states that "Medicaid, enacted under the federal spending power, “is much in the nature of a contract: in return for federal funds, the States agree to comply with federally imposed conditions.” He cites the 1981 Supreme Court case ruling in Pennhurst State School & Hosp. v. Halderman as the precedent for his argument.

"The Supreme Court has held and the Chief Justice said this, that the relationship between the federal government and the states under ACA is analogous to a contract and under traditional contract principles, when two parties agree to form a contract, they have lots of flexibility," Blumstein said in a phone interview with The Huffington Post.

"If one party unilaterally undertakes to change the contract in an unforseeable way, then there is an opportunity for unnecessary and excessive leveraging," he continued. "There was a bait and switch that the states could not have reasonably foreseen when they signed up for Medicaid originally."

Blumstein explained his brief's argument, citing an older lower courts case as an analogy. The 1902 case, Alaska Packers' Association v. Domenico, involved a group of sailors tied the hands of their employer by agreeing to their wages via contract, then notifying the landlocked employer while at sea that they refused to fish unless their wages were raised. "That's the contract rule," he said, "you can't take advantage of a party."

Blumstein's brief adds that "Acting at contract modification, [The Affordable Care Act Medicaid mandate] is coercive because it puts states to a set of choices that the federal government may not impose on states ... [it] also violates the Pennhurst clear-notice obligation because that obligation accrues in this case at contract formation, not contract modification."

Blumstein says he speaks for himself, not for any of his institutional affiliations. He insisted his brief was not politically motivated, and while he tends to support Republicans at the national level, he has worked for and voted for Democrats in the past, including voting for Al Gore, a former student of his, in the 2000 presidential election. He said he intentionally did not seek to have anyone join his brief.

"It's really my opinion as a health care scholar and a constitutional scholar," he said.

Blumstein has been a Vanderbilt law professor since 1970. He began expressing his concerns about the ACA's Medicaid Mandate in 2010, at the National Council of State Legislatures meeting, according to the Vanderbilt release. He then asked Florida state litigators to accept the Medicaid challenge and keep it in throughout the appeals as they made it to the Supreme Court.

"I think it's the right decision on this issue," he told HuffPost. "When the federal government asks the state to participate on a spending program, the states have to know what they're in for."