PHOENIX (CNN) — Arizona Democrats are calling Thursday for the Department of Justice to investigate what caused some voters to wait in line for five hours to participate in the Arizona primary.

Phoenix Mayor Greg Stanton requested that U.S. Attorney Loretta Lynch launch a federal investigation into the situation.

“Because of the unacceptably disparate distribution of polling locations, I respectfully request the U.S. Department of Justice investigate what took place in Maricopa County to ensure all voters are treated equally under the law,” he wrote Wednesday.

The Department of Justice has not yet publicly responded to Stanton’s request.

Voters endured long waits to use one of Maricopa County’s 60 polling stations Tuesday. There were at least 200 polling stations in 2012, but Republican officials said they decreased the number to save money.

Even after waiting in line for hours, some people were not allowed to vote. At least 20 Democratic voters contacted the Arizona Democratic Party to say that when they arrived at the polls, they were told that they were registered as Independents, and therefore unable to vote in the closed primary.

Arizona Gov. Doug Duce, a Republican, said Tuesday’s situation was “unacceptable.”

“If people want to take the time to vote they should be able to, and their vote should be counted,” he tweeted Wednesday, and asked election officials to figure out what went wrong.

“Our election officials must evaluate what went wrong. And how they (can) make sure it doesn’t happen again,” Ducey wrote.

Democratic Rep. Ruben Gallego said Thursday at a Phoenix press conference he thinks that changes pushed by Republican state lawmakers led to the voting problems.

“We need an independent investigation of what exactly happened, how did it happen, how are we going to prevent this in the future.”

Gallego called on Ducey to demand that his party make changes before future elections to prevent a similar situation.

“Let’s be clear — voter suppression happened on March 22. We don’t know at this point if it was by chance or by planning, but no matter what, there’s nothing we can do to deny that voter suppression happened,” he said. “Sitting and standing in line four to five hours to vote, even if you end up voting, is still voter suppression. And the fact that people are not questioning whether their vote is counted at all is also suppression.”

Historically, the Department of Justice had to approve any changes in voting procedure in Arizona because of the state’s history of discrimination against minorities in voting. But a Supreme Court decision in 2013 allowed Arizona to begin making changes without federal oversight. Leaders said if federal scrutiny had been required before making changes, Tuesday’s situation would have never happened.

Vermont Sen. Bernie Sanders, who lost Arizona to Democratic front-runner Hillary Clinton, called the situation “a disgrace.”

“In the United States of America, democracy is the foundation of our way of life,” the Democratic presidential hopeful said Wednesday. “And what happened in Arizona is a disgrace. I hope that every state in this country learns from that and learns how to put together a proper election where people can come in and vote in a timely manner and go back to work.”

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