The U.S. Supreme Court agreed on Friday to hear another case challenging a key piece of the Affordable Care Act. It could impact Arizonans who signed up for health insurance under the law and are getting federal tax credits.

Arizona is one of 34 states that never established a state health insurance marketplace, instead they used the federal site.

Here in Arizona, some 120,000 people used that system to buy insurance, and 77 percent of them got federal subsidies to help pay for it, according to data from the Department of Health and Human Services.

The original legislation, however, says that subsidies would apply to exchanges “established by the State.” The Internal Revenue Service later created a regulation to extend subsidies to plans bought on the federal exchange.

The challengers behind this lawsuit argue that those who purchased plans on the federal marketplace should not be able to receive those subsidies. 

The court is expected to rule on this case during the current term.

The news comes just a week before the second round of open enrollment for the Affordable Care Act begins on Nov 15.

In 2012 the Supreme Court upheld the law’s individual mandate.