Justice department warns that the practice of removing voters is illegal under federal law as Democrats call it discrimination

Florida says it will defy an order from the US justice department to stop purging its voter roll of people the state claims may not be American citizens.

The justice department has warned that the practice, which critics describe as "voter suppression" by Florida's Republican administration aimed at stripping the ballot from people more likely to support Democrats, is illegal under federal laws.

It has given the state until Wednesday to agree to halt the purge, something officials in Florida say they have no intention of doing.

Federal authorities say that the state is obliged to get justice department approval for changes to its voting laws under the 1965 Voting Rights Act, which was introduced to end practices that prevented African Americans from exercising their democratic right in many southern states.

The justice department also said that the purge appears to violate a federal law stopping voters being removed from the rolls less than 90 days before an election. Florida holds primaries in mid-August.

But Chris Cate, a spokesman for the Florida secretary of state, said the purge will continue.

"We have a year-round obligation to make sure the voter rolls are accurate. We are going to continue forward and do everything that we can legally do to make sure that ineligible voters cannot vote," he said.

The justice department move comes after the attorney general, Eric Holder, last week warned that gains of the civil rights struggle hang in the balance in the face of a determined effort by many states to roll back laws ensuring the right to vote.

He said that there is a "growing need to protect the voting rights of every eligible citizen" amid a flurry of legislation and executive orders in US states ostensibly to prevent election fraud with measures such as requiring proof of identity in order to vote.

Florida's governor, Rick Scott, has justified the purging of the voters roll as necessary to prevent fraud by people who are not American citizens. But there is little evidence that this has been a significant problem in the past and the effect has been to remove many people who are entitled to vote.

Although the numbers in Florida are relatively small they could prove important in November's presidential election. Barack Obama probably has to win the state if he is to hold on to office.

In 2000, George W Bush won the White House after taking Florida by a majority of just 537 votes leading to a bitter fight that went all the way to the supreme court amid accusations that the state authorities had weighted the system against his Democratic rival, Al Gore.

This year Florida has notified more than 2,600 registered voters that they may not be entitled to be on the electoral roll. The Miami Herald reported that in Miami-Dade County so far 385 people who were removed from the roll have been shown to be citizens while just 10 have not.

Those tasked with purging the rolls compares voter lists with driving licence files, which record citizenship. But critics say that system is flawed in part because many people obtain citizenship after applying for a driving licence.

Among those wrongly removed from the voter roll was Bill Internicola who was born in New York 91 years ago and earned a medal in the Battle of the Bulge during the second world war.

Florida authorities sent him a letter in May saying that it had received information that he was not a US citizen. The onus was then on Internicola and others who received similar letters to prove they have the right to vote. Internicola is a Democrat.

A Florida member of Congress, Alcee Hastings, described the state's purge of the electoral roll as "voter suppression".

The lone Democratic party senator in Florida, Bill Nelson, wrote to Scott saying that the move will be seen as an attempt to discourage ethnic minorities and the young from voting. Polls show they are more likely to support Democrats.

"Attempts to purge the voter roll so soon after signing one of the nation's most controversial voting laws raises concern, especially among young and minority voters," he said.

The Democratic party chairman in Florida's Broward county, Mitch Ceasar, acknowledged that the numbers of people affected are relatively small but said the purge of the voters roll is part of a broader assault in Republican-controlled states on voting rights.

"It's not by accident that Florida is doing this and all these other states that have Republican governors are doing it," he told the Miami Herald. "The odds are too high that they had the same independent thought of each other."

Last week, a federal judge struck down another part of Florida's recent election law which critics said was aimed at deterring voter registration groups from signing up electors.

The judge called the law "harsh and impractical" for requiring the groups to turn in registration forms within 48 hours of their completion or face large fines. The deadline was almost impossible to meet if the forms were sent in the post, as is common.

The League of Women Voters, one of the groups which took legal action over the law, said that the requirements had forced it to halt voter registration drives in Florida after 72 years.

In an editorial on Sunday, the Miami Herald called for an end to the purge of the voter roll, saying it was undemocratic.

It said that the Republicans claim to be preventing a problem that there is no evidence exists.

"It carries the stench of voter suppression in a presidential election year when Florida is among a handful of swing states key to victory for either President Obama or his Republican opponent, former Massachusetts Gov. Mitt Romney," it said.

"Florida seems to be heading back to those "Flori-duh" days of purging voters who have every right to vote and finding ways to limit young people, immigrants and minorities – who typically lean Democrat – from voting with onerous rules on voter-registration drives."