The US Supreme Court heard oral arguments Wednesday in Moore v. Harper, a case concerning the “independent state legislature” theory in redistricting cases.

The case concerns North Carolina’s congressional district map, created by the Republican-controlled legislature last year. North Carolina’s Supreme Court struck down the map as an unconstitutional gerrymander, and Republican lawmakers appealed to the US Supreme Court. The court denied an application for an emergency stay in March but ultimately agreed last June to take up the case.

The key argument for the groups is the “independent state-legislature theory.” The theory argues that the election clause, which states that elections must be “prescribed in each state by the legislature thereof,” gives exclusive power to state legislatures in drawing congressional maps.

During oral arguments Wednesday, David Thompson argued for the petitioners that “The Elections Clause requires state legislatures specifically to perform the federal function of prescribing regulations for federal elections. States lack the authority to restrict the legislatures’ substantive discretion when performing this federal function.” Several justices seemed skeptical of this position. Justice Elena Kagan cited several recent decisions, concluding: “Of course, state courts applying state constitutions typically constrain state legislatures when they redistrict, when they enact election laws.” When Thompson proposed a distinction between substantive and procedural limits on the legislature’s authority, Justice Amy Coney Barrett said, “those are kind of all notoriously difficult lines to draw.”

Neal Katyal argued on behalf of the Democrats who had challenged the map. He said, “the blast radius from [the Republicans’] theory would sow elections chaos.” US Solicitor General Elizabeth Prelogar also argued in support of the Democrats, allowing that there could be some room for federal oversight of state court decisions on electoral maps but urging the court to “adhere to the consistent practice that has governed for more than two centuries and … reject Petitioners’ atextual, ahistorical, and destabilizing interpretation of the Elections Clause.”

A decision in this case is expected in June.