Washington (AFP) - The US Supreme Court appeared sharply divided on Wednesday as it heard a case that could fundamentally alter the way elections for the White House and Congress are conducted.

The case brought by Republican lawmakers in North Carolina would potentially give state legislatures sole authority in deciding who votes, where and how in federal elections.

The prospect has raised concerns for democracy on the left -- and to a lesser extent on the right -- in a bitterly divided country still reeling from Donald Trump's refusal to accept the 2020 election results.

The three liberal justices on the nation's highest court appeared deeply skeptical as they heard oral arguments from a North Carolina lawyer in favor of what is known as the "independent state legislature" doctrine.

At least three of the six conservative justices seemed sympathetic, while it was unclear where the other three stood.

Under the Constitution, the rules for federal elections are set by state legislatures. 

"The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof," the Elections Clause says. It gives Congress, however, the power to "alter such Regulations."

State legislatures have used their authority to map congressional districts, set poll hours and agree on rules for voter registration and mail-in and absentee ballots.

They have also, at times, engaged in what is known as partisan gerrymandering -- drawing up congressional districts to favor a particular political party.

Their laws have been subject, however, to scrutiny by the state courts and North Carolina's Republican lawmakers are seeking to do away with that judicial input.

"Our position is the checks and balances do apply," said David Thompson, a lawyer representing North Carolina lawmakers. "We've got the political check that the founders envisioned of going to Congress."

Conservative Justice Samuel Alito appeared to back up that argument.

"No matter what we say the Elections Clause means, Congress can always come in and establish the manner of conducting congressional elections," Alito said.

'Big consequences'

Justice Elena Kagan, one of the three liberals on the court, warned that the "independent state legislature" doctrine could have "big consequences."

"It would say that if a legislature engages in the most extreme forms of gerrymandering there is no state constitutional remedy for that, even if the courts think that that's a violation of the Constitution," Kagan said.

"It would say that legislators could enact all manner of restrictions on voting," she added. "It might allow the legislatures to insert themselves, to give themselves a role in the certification of elections.

"What might strike a person is that this is a proposal that gets rid of the normal checks and balances on the way big governmental decisions are made in this country," she said.

"And you might think, that it gets rid of all those checks and balances at exactly the time when they are needed most."

Representing the Biden administration, Solicitor General Elizabeth Prelogar warned that accepting the "independent state legislature" doctrine would "wreak havoc" in the running of elections and "sow chaos on the ground."

"State and federal elections would have to be administered under divergent rules," Prelogar said. "And federal courts, including this court, would be flooded with new claims."

'Nonsense'

The case, Moore v. Harper, stems from an electoral dispute in North Carolina.

The 2020 census found that the state's population had increased, earning it an extra seat in the US House of Representatives.

North Carolina lawmakers redrew the congressional map to add a new district but the state supreme court threw it out, arguing that it favored Republicans by grouping Democrats in certain districts, diluting their vote.

North Carolina lawmakers appealed to the Supreme Court arguing that local courts were usurping their authority.

Democrats, from the state level to President Joe Biden, law professors and leading civil rights organizations filed briefs urging the Supreme Court to reject the doctrine, while the Republican Party dismissed the criticism as "nonsense."

The court is to deliver its ruling by the end of June.