The "review" was prompted by a letter sent Monday by Sens. Lindsey Graham and Jim DeMint to Attorney General Henry McMaster, who is currently running for governor. "We have serious concerns about the constitutionality of this Nebraska compromise as it results in special treatment for only one state in the nation at the expense of the other 49," they wrote (.pdf).
In an interview with McClatchy, DeMint said the Nebraska provision, which would save the state $100 million, violates Article 1, Section 9 of the Constitution: "No preference shall be given by any regulation of commerce or revenue to the ports of one state over those of another ..."
But it seems more likely that the criticism is an opportunity for attorneys general with higher political ambitions to make hay out of the health care bill. In his own statement (.pdf) on the effort, McMaster emphasized that the provision was unfair:
"Quite obviously, this issue raises very serious concerns about equity, tax fairness as well as the constitutionality of having federal tax levies and mandates that treat one state differently from all the others."
He told McClatchy that state AGs wouldn't have standing to sue until the bill is signed into law.