Officials in Arizona are asking the US Department of Justice to investigate the lack of polling stations in poor or minority areas during the state’s primary.
Voters in Maricopa County experienced long waiting times during the presidential primary, and some people were turned away after waiting.
In some spots across the county, voters waited for up to five hours on Tuesday.
Governor Doug Ducey, a Republican, called the queues “unacceptable”.
“Our election officials must evaluate what went wrong. And how they can make sure it doesn’t happen again,” Mr Ducey said on Twitter.
In 2012, the county – which includes Phoenix, the state’s largest city – had 200 polling places.
Phoenix is a predominately Democratic area. In Maricopa County, about 1.2 million people are eligible to vote, but there were only 60 polling places.
Arizona’s Republican-led legislature decided to lower the number of polling places to save money, officials said.
Democratic presidential candidate Bernie Sanders called the queues a “disgrace” and has expressed concerns that the long lines hurt his showing in the state.
Rival Hillary Clinton won the state by 18 percentage points.
In the past, the federal government would have to approve any changes made to Arizona’s election rules because of the state’s history of discriminating against minority voters.
However, a 2013 US Supreme Court decision that did away with much of the Voting Rights Act, allowing Arizona and other states to adjust voting rules without oversight.
Phoenix Mayor Greg Stanton said he wants the Justice Departments investigate whether elections officials illegally cut polling stations in poor and minority-concentrated areas.
He wrote in a letter to the Justice Department that elections officials and the state lawmakers have created “a culture of voter disenfranchisement”.
State lawmakers said they plan to meet to discuss the voting mishaps.
Arizona resident Bruce Weiss said he waited two hours at a polling place in Phoenix. Many did not get into the polling places until after midnight.
“It’s like a complete, total failure of government,” he told the AP news agency.
Maricopa County top election official Helen Purcell initially blamed voters, then took it back, accepting responsibility for the long queues.
Officials said they had more mail-in ballots than usual and were expecting less in-person voters.
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