US President Joe Biden has likened a new voting law in the state of Georgia to racist policies of the 20th Century US South, calling it an "atrocity".
The law adds restrictions to voting that Mr Biden said disproportionately targeted black Americans.
Republicans say they are streamlining voting procedures and trying to restore confidence in the election system.
The president called the law "Jim Crow in the 21st Century" and "a blatant attack on the Constitution".
Jim Crow refers to the 19th and 20th Century laws that enforced racial segregation in the South.
In last year's presidential election, Mr Biden became the first Democratic candidate to win Georgia since 1992 - and it was high turnout among black Americans that was believed to have tipped the state in his favour.
What did President Biden say?
In his statement, released on Friday, Mr Biden said: "Recount after recount and court case after court case upheld the integrity and outcome of a clearly free, fair, and secure democratic process.
"Instead of celebrating the rights of all Georgians to vote or winning campaigns on the merits of their ideas, Republicans in the state instead rushed through an un-American law to deny people the right to vote."
He added: "This law, like so many others being pursued by Republicans in statehouses across the country, is a blatant attack on the Constitution and good conscience."
He later added that the justice department was "taking a look" at the new Georgia laws.
What does the new law do?
The Election Integrity Act of 2021 passed in both chambers of the state's Republican-controlled legislature on Thursday.
It makes Georgia the second state to pass laws that restrict ballot access in the aftermath of the 2020 election.
The key elements of the legislation:
- Ensure new ID requirements for requesting mail-in ballots, replacing the current system which simply requires a signature
- Ban the practice of giving food or water to voters in line at polling stations
- Give the state legislature more power to take control of voting operations if problems are reported
- Limit the number of "drop boxes" in which people can place their absentee votes, meaning many will have to travel further
- Shorten the early-voting period for all runoff elections
Why are the two sides clashing on this?
Georgia is one of more than 40 states in which Republicans are pushing for a tightening of rules around voting, mainly targeting those who do not vote on the day at polling stations.
Although there was no evidence of widespread fraud in the last presidential election, many Republican voters have supported ex-President Donald Trump's unfounded allegations of voting irregularities. One survey last month showed 67% of Republicans thought the presidential election was invalid.
Republicans say they are simply streamlining the voting and counting procedures to ensure election integrity.
The Democrats say it is an attempt to target social and ethnic groups who are more likely to vote for them, reducing the surge in votes from those groups in the last election.
On requiring new ID for mail-in ballots, they say it will now be harder for working-class people - who may not have an ID - to cast a ballot.
Republicans say giving food or water to voters in line is a method of soliciting votes. Voters, particularly in majority black parts of the state, have often had to wait in line for hours.
Democrats say shortening the period for run-off elections from nine weeks to four is an attempt to suppress votes, after an energised voter base in Georgia sent two Democrats to the US Senate this year - giving the party effective control of the upper chamber.
Republicans say it will more fairly reflect voters' beliefs at the time of the initial vote.
Mr Trump issued a statement after the Georgia move, saying: "They learned from the travesty of the 2020 presidential election, which can never be allowed to happen again. Too bad these changes could not have been done sooner!"
Mr Trump had repeatedly pressured Georgia's secretary of state, Brad Raffensperger, in January, urging him to "find" votes.
Mr Raffensperger, who has staunchly defended the integrity of the state's votes, also backed the new laws.
"The cries of 'voter suppression' from those on the left ring as hollow as the continuously debunked claims of 'mass voter fraud' in Georgia's 2020 election," he said.
But influential Democrat Stacey Abrams, who helped mobilise the black vote in Georgia, shared Mr Biden's view: "Suppression is the lazy man's way of winning an election. If you can't win honestly, push people out of the game, change the rules."
Democratic state lawmaker Park Cannon was arrested and removed from the state capitol for banging on Governor Brian Kemp's office door as he signed the bill.
"Georgia will take another step toward ensuring our elections are secure, accessible and fair," Mr Kemp told reporters while signing it.
What will happen in other states?
Georgia has now joined Iowa in passing some form of overhaul to voting rules.
They probably won't be the last. There are currently 253 similar bills in 43 states, according to the left-leaning Brennan Center for Justice think tank.
That's because, while Democrats currently hold slim majorities in both chambers of the US Congress, Republicans dominate state legislatures.
Data from the National Conference of State Legislatures shows Republicans have legislative control in 30 states and unified control - including the governorship - in 23 states, far more than Democrats.
Unified control means that what happened in Georgia - where a law quickly passes both chambers and gets signed by the governor - can easily be replicated.