It was unclear what the court would do with other aspects of the law that have been put on hold by lower federal courts.
Romney swept Connecticut, Rhode Island, Delaware and Pennsylvania, and is expected to win New York shortly.
The GOP candidate indicated that he agreed with President Obama that interest rates should remain low.
Two-thirds of state Republican Party chairs and members of the Republican National Committee say Sen. Rob Portman (R) is both the best and most likely veep pick for Mitt Romney. But it's still early.
Sen. Orrin Hatch is favored to win reelection, but first he faces a primary election against tea party favorite Dan Liljenquist. Can Hatch avoid the fate of former Utah Sen. Bob Bennett, ousted in 2010 by the tea party?
The Cuban-American senator may be considering a presidential run in 2016, however.
Leading Republicans are concerned about entering the 2016 race as a loser.
Beth Myers has been with Romney's various campaigns since his days as Governor of Massachusetts, and has a reputation for detail.
Mitt Romney trails President Obama by 40 points among Latinos, a new Pew poll shows. Maybe Marco Rubio, the charismatic US senator from Florida, can help by introducing a new version of the DREAM Act.
There will be no Sarah Palin or Dan Quayle-like surprises from Romney's VP, sources say.