A Wisconsin judge has struck down a controversial voter ID law passed by governor Scott Walker, which would have required voters to show photo identification at the polls.

Dane County circuit judge Richard Niess issued the permanent injunction one week after another judge temporarily stopped the law.

Niess found the law to be an unconstitutional abridgement of the right to vote, effectively disfranchising eligible voters without ID. He argued that while Governor Walker and the state legislature have the power to enact election laws, their constitutional authority was exceeded by eliminating the right to vote for some eligible voters.

"Without question, where it exists, voter fraud corrupts elections and undermines our form of government," wrote Niess in his eight-page decision. "The legislature and governor may certainly take aggressive action to prevent its occurrence. But voter fraud is no more poisonous to our democracy than voter suppression. Indeed, they are two heads on the monster."

Niess added that those disfranchised by the law would include "struggling souls" who – though constitutionally entitled to vote – lack the resources to comply.

"A government that undermines the very foundation of its existence – the people's inherent, pre-constitutional right to vote – imperils its legitimacy as a government by the people, for the people, and especially of the people," he added.

The Wisconsin decision comes a day after the justice department blocked a similar photo ID law in Texas signed by governor Rick Perry. According to data submitted to the DOJ, registered Hispanic voters in the state stood a significantly stronger chance of being denied the right to vote as a result of the law.

The recent decisions reflect a nationwide debate on the propriety of US voter ID laws. Fifteen states currently have voter ID laws on the books. Meanwhile legislation in 31 states includes proposals to introduce voter ID laws or strengthen existing ones. A recent report by the Brennan Center for Justice found that since last year an estimated 5 million eligible voters were stripped of their right to vote.

On Wednesday, leaders from the National Association for the Advancement of Colored People will appeal to the United Nations human rights council, arguing that a systematic attempt to disfranchise millions of black and Latino voters is under way in the United States.

Headed by president Ben Jealous the NAACP will call on the UN to launch a formal investigation into the spread of restrictive voting laws, particularly in the southern United States. While the UN is not empowered to compel individual US states to alter their voting laws, the NAACP hopes the council will be able to shame them into making changes that enfranchise more voters.

Wisconsin's law is currently challenged by four pending lawsuits; two at the state level and two at the federal level. Monday's suit was brought by Melanie Ramey and the Wisconsin League of Women Voters in November.

"We felt that it was our duty to pursue this case," said Ramey, who is president of the League. "We're very pleased [with the decision]. We felt that it was a violation of the constitution of this state."

Ramey believes Neiss's decision will stand up to any appeal from the state government, and added that the rights of roughly 200,000 eligible Wisconsin voters were endangered by Governor Walker's law.

The American Civil Liberties Union of Wisconsin is currently pursuing one of the federal cases against the law. The ACLU seeks to challenge governor Walker's law on constitutional grounds and on the basis of section 2 of the Voting Rights Act, which prohibits discriminatory voting practices or procedures on the basis of race, color or membership in a minority group.

"Both approaches are important," says Chris Ahmuty, executive director for the ACLU in Wisconsin. According to Ahmuty, the decision "demonstrates how vulnerable the law is".

A statement issued by Wisconsin attorney-general JB Van Hollen argued the law is "consistent with the constitution" and indicated he would appeal. The decision comes less than four weeks before voters head to the polls for Wisconsin's presidential primaries and local elections, making the prospect of an appeal more difficult.