The Supreme Court has set a hearing for March to take up a new, high-profile challenge to ObamaCare. 

The court announced Monday that it will hear the case on March 4, 2015. The move comes after the court first announced in November it would take up the challenge. 

At issue in the case is the legality of subsidies offered to help millions of low- and middle-income people buy health insurance. 

Opponents argue that most of the subsidies are illegal. They have challenged the legality of providing them in states that do not have their own insurance exchanges -- in other words, those using 

In July, a Richmond, Virginia-based appeals court upheld Internal Revenue Service regulations that allow health-insurance tax credits under the Affordable Care Act for consumers in all 50 states. 

On that same July day, a panel of appellate judges in Washington, District of Columbia, sided with the challengers in striking down the IRS regulations. The Washington court held that under the law, financial aid can be provided only in states that have set up their own insurance markets, known as exchanges. 

The administration has said the congressional intent behind the law is for eligible customers regardless of where they live to receive assistance from the government to subsidize the purchase of health care. 

Though the case could mark the biggest challenge to the law since it was narrowly upheld in 2012, the White House has said such cases "won't stand in the way" of the Affordable Care Act. 

The Associated Press contributed to this report.