A judge in Pennsylvania struck down one of the most restrictive voter identification laws in the country on Friday, in a victory for civil rights campaigners who are seeking to block voter eligibility rules they claim are discriminatory.

Commonwealth court judge Bernard McGinley concluded the state's voter ID law, introduced by Republican-controlled state legislature in 2012, disenfranchised “hundreds of thousands” of voters who could not easily meet the requirements set by the state.

“Voting laws are designed to assure a free and fair election; the voter ID law does not further this goal,” the judge said, adding: “Disenfranchising voters through no fault of the voter himself is plainly unconstitutional.”

The new law required voters to present photo identification proving their eligibility to vote, replacing other proof-of-address documents such as paychecks or bills. Photo identification had proven difficult for many voters to obtain, despite the state's promises to the contrary.

In one particularly damning section of his ruling, Judge McGinley found there was no evidence the legislation was even intended to stamp out voter fraud, which was the justification given by state lawmakers when they passed the law.

Although the ruling was a significant one for Pennsylvania’s 8.2 million voters, legal scholars said it had only limited implications for the rest of the country, where similar laws have passed from state to state.

The crux of the ruling was that Pennsylvania had failed to fulfil its promise of providing “liberal access” to a photo identification that would be accepted at the ballot box.

“My initial reading is that this is a great victory for opponents of voter ID laws, but it is very state-specific,” said William Yeomans, a former chief of staff in the Justice Department who is now a professor at American University in Washington.

“One very important thing is the court seemed to reject the bogus argument that the law was aimed at preventing voter fraud,” he added. “That will have some broader resonance.”

Yeomans was involved in the development of a new, bipartisan bill, unveiled in Washington on Thursday, that would restore parts of the Voting Rights Act that was controversially knocked down by the supreme court last year.

The bill would enact a new formula to determine which states should be subject to special scrutiny by federal authorities.

However, its provisions relating to the contentious issue of voter ID requirements were significantly watered down in order to mollify Republican lawmakers, whose support is critical for the legislation to succeed.

No evidence of party bias

McGinley said there was no evidence Pennsylvania's law was intended to prevent voter fraud.

Civil rights experts argue that, in Pennsylvania and elsewhere, unreasonably burdensome requirements for voting have been introduced over the last decade in the knowledge they will discourage or impede elderly, low-income or minority voters, who tend to vote for Democrats.

In a footnote to his ruling, McGinley expressly discounted this allegation, stating there was “no evidence that the purpose behind the voter ID law was to disenfranchise minorities or persons who … may be more inclined to vote for Democratic candidates”.

In a ruling otherwise supportive of the law's opponents, the judge said he did not believe it violated equal protection rights, enshrined in state and local law.

Campaigners and lawyers involved in the legal action were nonetheless buoyed by the outcome. “Judge McGinley issued a devastating indictment of the Pennsylvania voter ID law,” said Michael Rubin, a Washington-based attorney involved in the case.

“He found that not everyone who wants an ID can get one. He dispelled the myth that photo ID is commonplace, and everyone in society who needs one has one. He found the law is invalid on its face, had no legitimate purpose [and] does not further the goals of free and fair elections.”

The voting rights issue is especially salient in a state like Pennsylvania, a potential swing state with a large number of electoral college votes in presidential elections.

Enforcement of the Pennsylvania's photo ID requirement had already been halted by earlier court orders pending resolution of the constitutional challenge. It is not known whether, if the supreme court hears the case, a ruling will be issued before primary elections in May.

Difficulties obtaining photo IDs

Pennsylvania’s voter ID law raised the bar for voters, requiring them to present specific forms of photo identification. Previously, voters had been able to participate in the elections by showing other forms of documentation, such as utility bills or paychecks.

To aid the process, state authorities had promised to make it easy for voters to obtain other forms of ID that would enable them to vote. However, the judge found that, despite the creation of 71 locations that issued the documentation, it remained prohibitively difficult for many voters to obtain the required identification.

Because the ruling focused largely on Pennsylvania's inability to meet its promises, rather than tackling more fundamental issues, it is unlikely to serve as a precedent for other similar challenges to voting ID laws in Texas, North Carolina and Wisconsin.

Richard Hasen, a University of California professor whose latest book examines the so-called voting wars that have swept the US since 2000, said the ruling’s wider implication is “somewhat limited”. “The findings on implementation are state-specific and don’t really carry over to other states,” he said.

Still, the case does not bode well for other states seeking to defend tough eligibility requirements at the ballot box, which is generally justified as an attempt to prevent fraud.

“The commonwealth, starting in 2012 when we filed this lawsuit, was unable to identify a single instance of the kind of voter fraud that legislators and proponents of these voter ID laws claimed was going on,” said Witold Walczak, from Pennsylvania’s branch of the American Civil Liberties Union.

“When you look at it that way, the only fraud that is being perpetrated here in Pennsylvania is by the people who support this voter ID law.”