By KATE ZERNIKE

In a swipe at President Obama’s signature health care legislation, Gov. Chris Christie of New Jersey vetoed on Thursday an online marketplace that the Legislature created to help middle-class residents buy health insurance.

Under the Affordable Care Act, the federal law passed in 2010, all individuals must have health insurance, and states must create the so-called health care exchanges to help them buy it.

In his veto message, Mr. Christie referred to the pending Supreme Court challenge to the law and said the exchange would impose “unnecessary obligations upon the state’s citizens.”

“Indeed, the very constitutionality of the Affordable Care Act is cloaked in uncertainty, as both the individual mandate to procure health insurance as well as the jurisdictional mandate to establish an exchange may not survive scrutiny by the Supreme Court,” Mr. Christie wrote. “Because it is not known whether the Affordable Care Act will remain, in whole or in part, it would be imprudent for New Jersey now to create an exchange before these critical threshold issues are decided with finality by the court.”

Mr. Christie was the second governor to veto such a measure, following Gov. Susana Martinez of New Mexico, also a Republican.

The veto is largely symbolic: the law required states to set up health care exchanges, but provided that the federal government would step in to create them in states that failed to do so. In either case, the state pays to set up the health care exchange, even though states that fail to set up the exchanges lose the ability to tailor them.

Assemblyman Herb Conaway, a doctor and the lead sponsor of the legislation in New Jersey, said the governor was sending a message that “he doesn’t care” about the 1.3 million state residents without health insurance.

“I am disappointed that Governor Christie put national political pressures ahead of the well-being of New Jersey,” said Dr. Conaway, Democrat of Burlington County. “His actions have once again shown his complete disregard for our most vulnerable populations.”