On Tuesday, the Department of Justice filed a lawsuit against Florida over its voter purge program aimed at removing non-citizens from voter rolls. We’ve taken a closer look at the controversy surrounding the program and why the federal government has gotten involved:

So what is Florida doing and why is it so controversial?

Florida has compiled a list of potential non-citizen registered voters using data provided by the Florida Department of Highway Safety and Motor Vehicles. It has sent the list to county election supervisors and requested that the supervisors contact flagged voters to verify their citizenship.

In its suit, the Justice department has claimed the data is “outdated and inaccurate” and may mistakenly identify registered voters who are U.S. citizens, depriving them of their right to vote. In response, Florida Gov. Rick Scott has reiterated his support for the initiative, which he says is necessary to preserve the integrity of voting rolls.

Isn’t it important to perform such voter roll purges to make sure voter lists are up-to-date?

Yes, every state must go through its voter rolls in order to account for death, relocation out of state, or change in eligibility due to a criminal conviction or mental incapacitation. (Read more about purge practices in this 2008 report).

And of course, only U.S. citizens are eligible to vote in this country.

Florida is not the first state to flag the issue of non-citizen voting: both New Mexico and Colorado have taken similar steps. But Florida’s efforts—directing county officials to purge suspected non-citizens from the voter rolls—are getting extra attention because it’s happening so close to a presidential election.

Florida officials say they’re ordering the purge because of concerns about voter fraud. Such voting fraud appears to be quite rare, perhaps because the penalties are strict—it’s a felony in Florida and many other states—and the payoff relatively modest (a single vote). A 2007 report by the Brennan Center for Justice found very few cases. The report suggested that what was thought to be fraud was more often a result of registration error or other mistakes.

How many non-citizen voters has Florida found?

One hundred and five, according to Chris Cate, spokesman for the Florida Department of State. Those are non-citizens who are registered to vote. Fifty-six of them have “a voting history,” said Cate. He could not provide the number of times these people cast a ballot. Florida has 11 million registered voters.

How many U.S. citizens are at risk of being purged from the voter roll?

It’s not clear.

Some news reports place the number at 500. (Here is a profile of one of the most widely publicized cases.)

Election supervisors in every county have been instructed to send a form letter notifying a person that he or she has been flagged by state driver’s license records for suspect eligibility and must send in proof of citizenship (a U.S. passport, birth certificate or naturalization papers). If a person fails to respond within 30 days, a public notice is published in the newspaper. If another 30 days pass with no response, election supervisors can remove that person from the voting rolls.

That gives flagged voters a total of 60 days to object. And isn’t this all happening pretty close to the elections?

Yes, it’s a tight timeframe and that’s why the Justice Department says it’s suing.

The federal National Voter Registration Act of 1993 prohibits any action designed to adjust voter registration status 90 days before any federal election. As the government has pointed out, Florida holds its primary election for both parties on August 14 — less than 90 days away.

One provision of the law is meant to safeguard against potential error and give residents ample opportunity to challenge any false registration claims well before they head to the polls. That required 90-day window has appeared in litigation between other states and advocacy groups in previous years.

Are county officials following through on the purge?

No, only a few are.

Most of the election supervisors in Florida are opposed to the state’s voter purge initiative and have said they won’t follow through on it.

Palm Beach County Supervisor of Elections Susan Bucher, for instance, has refused to contact any of the 115 suspected non-citizens in her county after observing that some of their interactions with the DMV dated as far back as 12 years.

“We knew the information was old,” Bucher told ProPublica.

Earl Lennard, an election supervisor in Hillsborough County, said his office wouldn’t contact any more flagged residents “without any corroboration or additional information.”

Moreover, the general counsel for the Florida State Association of Supervisors of Elections has recommended supervisors refrain from taking any further action until the government’s lawsuit is resolved.

If Florida is being too rushed, is there a better way to do it?

It depends whom you ask. The problem with state driver’s license records is that citizenship status can change without the DMV’s knowledge. A non-citizen who obtains a driver’s license and happens to register to vote at that time can become naturalized down the road. This new information won’t be reflected in DMV records unless that person later returned to renew their license.

The Florida Department of State acknowledges these potential limitations and has therefore sought to gain access to a federal database known as SAVE, for Systematic Alien Verification for Entitlements. That database provides immigration status information to federal, state, and local agencies to determine eligibility for public benefits and licenses. The Department of Homeland Security, which maintains the database, has refused to turn over the data; a June 11 Justice Department letter to Florida officials claims they must first give DHS more information about residents. Florida actually sued the federal government on Monday to get the data.

In interviews, Gov. Scott has accused the federal government of stonewalling his request, first made in September 2011.

That raises the question of why Gov. Scott’s administration has chosen to focus on this initiative now. Florida has been a key swing state, if not the decider, of past presidential elections. According to the Miami Herald, many of the voters flagged during the process have been registered independent. The Herald also reports that the voter purge was on Scott’s mind ever since early last year. Then-Secretary of State Kurt Browning told the paper he was reluctant to implement the initiative because “we didn’t have our I’s dotted and T’s crossed when I was there.”

“I wanted to make sure the data was good if it went out under my name,” Browning told the Herald.

Hasn’t there also been controversy over voter suppression in Florida?

Some critics of the voter-purge initiative say this is just one of a series of steps Gov. Rick Scott has taken to curtail voting rights. Within the last year, Florida has shortened the time frame for early voting, imposed tougher restrictions on voter registration drives and made it more difficult for released felons to regain the right to vote.  One Florida senator has compared the latest initiative with the state's  improper removal of 1,100 eligible felons from voter rolls prior to the 2000 election. 

The more stringent voting requirements are part of a national trend. Since early 2011, 41 states have introduced bills outlining more restrictive measures on voting procedures.