The U.S. Supreme Court is preparing to release a decision on President Obama's signature healthcare law, one of its biggest rulings "in the last 50, 60 years."

Besides shaking up the 2012 presidential race, the case will define the legacies of Obama and of Supreme Court Chief Justice John Roberts -- and shape the future of the U.S. healthcare system, The Hill reported.

"We're keeping a close eye on it. Absolutely. We're having a war room ... every Monday and Thursday," Rep. Diana DeGette, D-Colo., said.

"Nothing I can do about it; it'll come when it comes," Rep. Allen West, R-Fla., said. "It's kind of like waiting to go into a firefight. You don't want to be too anxious to do it."

The case is a landmark decision on the breadth of Congress' constitutional power and will rival some of the Supreme Court's most important decisions ever, one lawmaker told The Hill.

"It's huge," Rep. Phil Roe, R-Tenn., a doctor and healthcare law critic, said. "I think it's one of the biggest decisions the court has made in the last 50, 60 years -- Brown v. Board of Education [on school desegregation], Roe v. Wade [on abortion], the 2000 presidential election [between George W. Bush and Al Gore]; those are all big decisions, and this is one of them."

Twenty-six states and the National Federation of Independent Business challenged the healthcare law, contending its individual mandate requiring most taxpayers to buy insurance or pay a penalty is unconstitutional. If the court agrees with the argument, it also must decide whether to void the entire law or only part of it.