Civil liberties campaigners filed an emergency motion on Monday to stop Wisconsin’s “disenfranchising” new voter identification requirements from going into effect, setting up an instant showdown after the US supreme court turned away an appeal to throw out Wisconsin’s controversial law that forces people already registered to vote to show photo ID.

If the emergency filing by the American Civil Liberties Union fails and Wisconsin fully activates its voter ID laws, the high court’s non-decision could affect an estimated 300,000 voters in that state – with sweeping voting-rights implications nationwide.

Now that the supreme court has declined to take the Wisconsin case, brought by the ACLU and other groups, the justices could be presented later this year with cases from either Texas or North Carolina, where similar laws are being challenged in local courts.

“Permitting these laws to go into effect and disenfranchising thousands of voters casts a cloud on the integrity of our democracy, especially as we head into the 2016 presidential election,” said Dale Ho, director of the ACLU’s voting rights project. “It’s a disgrace.”

Long denounced by activists as a “recipe for chaos”, the law in Wisconsin was originally passed in 2011 and has bounced back and forth between opposing decisions by various courts. The measure was only in force for one actual local election, until it was blocked temporarily by the supreme court just before November’s midterm elections.

Now the supreme court has declined to take up the case, lifting the temporary block on the law. Should the ACLU’s move in response fail to put that block back in place, a lower court’s ruling that the law is constitutional will stand in the state, affecting 10% of registered voters in the state, according to the ACLU’s calculations.

The new law is being driven by Wisconsin’s conservative governor – and presumptive presidential candidate – Scott Walker and his fellow Republicans, claiming it prevents voter fraud.

Walker previously dismissed the argument that there was almost no evidence anywhere of voter fraud in the form of people turning up at a polling station pretending to be someone else, saying even one illegal vote deprived genuine voters of their rights.

Democrats argue that the law is really aimed at sections of the population that tend to vote for their party and also find it hardest to get a state-issued photo identification card, because of expense or difficulty in producing the necessary documents, such as a birth certificate to get a driving license.

The ACLU has filed the emergency motion to suspend the law again because there are local elections coming up in Wisconsin in April and early voting has already begun.

Ho pointed out that when a new voter ID law was approved in Indiana in 2008, that state and Georgia were the only ones to require that additional photo ID be shown by registered voters, and there were exceptions to the rule.

Since then, 26 states have tightened their voter ID laws, with 10 of those being especially stringent, according to the ACLU, such as requiring photo ID without exception.