In the latest exchange of fire in an increasingly fierce war over voting rights in the United States that risks distorting the outcome of this year's presidential election, the US Justice Department has served notice to Florida that it is breaking the law by attempting to "cleanse" its voter rolls of foreign citizens.

Florida is in the vanguard of a group of states, most of them controlled by Republicans, taking steps to tighten eligibility requirements for citizens intending to vote in November in the name of eliminating fraud from an electoral system they say is hopelessly faulty. Democrats and civil rights advocates, on the other hand, say it is part of a grand design to suppress voting among constituencies likely to favour President Barack Obama.

The result of 24 laws passed in 19 states – including five critical states that will decide if Mr Obama or Mitt Romney pockets the keys to the White House – could be to disenfranchise as many as five million potential voters, according to the Brennan Centre for Justice at New York University.

Nowhere is the fight more intense than in Florida, the swing state which threw the 2000 presidential vote into disarray: George W Bush, the eventual victor, and Al Gore were separated by barely 500 votes.

The sitting Republican Governor, Rick Scott, has initiated an array of voting reforms. They include restrictions on early voting which have crimped the efforts of black churches to encourage congregants to participate. Governor Scott has also overseen measures to ensure that up to a million voters who have been convicted of crimes cannot vote, even if they have served their time. A large majority are African-Americans.

Equally controversial has been a push by the Sunshine State to make use of data compiled by the Department of Homeland Security to root out foreign citizens who might vote in November when they should not. It is this so-called "purge" of the rolls – which so far has unearthed only one Ecuadorian man who voted illegally in 2008 – that has drawn the ire of the Justice Department.

In a submission to the federal district court in Tampa, lawyers for the government argued that, under the Voting Rights Act of 1965, Florida was obliged to seek the approval of the federal authorities before embarking on the purge, something it has not done.

Another state under the microscope is Pennsylvania, which has passed new laws that will bar anyone without government-issued ID from voting. As many as 750,000 voters will find themselves unable to participate on 6 November, most of them in Philadelphia, a Democrat stronghold.

The Republican claim that these changes will not undermine the Voter Rights Act but will rather return integrity to the system were exposed as less than honest by the leader of the Republicans in the Pennsylvania state legislature, Mike Turzai. He told a group of supporters recently: "Voter ID, which is going to allow Governor Romney to win the state of Pennsylvania. Done!"

Belfast Telegraph