The ballots are printed, election workers trained and voting locations scouted. But with just a month to go before Election Day, the rules under which the midterms will be conducted remain in flux in four key states.

The outcomes of legal challenges could determine just who is eligible to vote on Election Day — and, in states where Senate and gubernatorial races are nail-bitingly close, just who wins when the votes are counted.

In Wisconsin, voting rights advocates have appealed to Supreme Court Justice Elena Kagan, seeking an injunction to halt the state’s voter identification measure. A federal district court in Texas is weighing whether to block a voter identification law after hearing arguments last week. Justices on the Arkansas Supreme Court heard arguments Thursday over the constitutionality of a similar law.

And North Carolina officials are seeking an injunction from the U.S. Supreme Court after the 4th Circuit Court of Appeals ruled this week that the state must allow eligible residents to register and vote on the same day, and to cast provisional ballots if they show up at the wrong precinct.

A case in another state, Ohio, was temporarily resolved this week when the U.S. Supreme Court issued an order allowing the state to cut the number of early voting days from 35 to 28. The decision, an injunction reversing a lower court’s ruling against the state, eliminates the state’s “Golden Week,” when voters could both register and vote at the same time.

The four states where litigation is pending are all the more important because of closely-fought contests in each. Wisconsin Gov. Scott Walker (R) narrowly leads his opponent, Madison school board member Mary Burke (D); Arkansas Sen. Mark Pryor (D) is in a tough fight against Rep. Tom Cotton (R), and both parties are battling for an open governor’s mansion; North Carolina Sen. Kay Hagan (D) holds a slim advantage over her opponent; and in Texas, Rep. Pete Gallego (D) and his Republican opponent are weathering hundreds of thousands of dollars in outside spending.

The cascade of court cases, experts say, is occurring because of the proximity of Election Day and amid confusion over just how to interpret two earlier Supreme Court cases: One, in 2008, upholding Indiana’s voter identification law and another, in 2013, invalidating parts of the Voting Rights Act.

“We’re in a situation where the courts have to act before an election, so everything gets jammed up,” said Rick Hasen, a professor at the University of California-Irvine and author of the Election Law Blog. “We’re hitting peak election litigation season.”

Voting rights groups like the American Civil Liberties Union and The Advancement Project have brought suit in the three states where voter identification laws are set to go into effect.

“A lot of people are going to be effected by this. Is it going to be enough to change the outcome of the election? I don’t know,” said Dale Ho, director of the ACLU’s Voting Rights Project.

The number of voters impacted could top one million: About 300,000 registered voters in Wisconsin do not have a proper form of identification, a district court found. Plaintiffs estimated 800,000 Texans don’t have the right form of identification. And about 20,000 people used same-day voter registration to cast ballots in North Carolina in 2012, and a similar number is expected this year, if the 4th Circuit ruling stands.

Time is of the essence. In Wisconsin, those groups say the fact that the 7th Circuit Court of Appeals ruled only this week to allow the state to implement its 2011 voter identification law does not give hundreds of thousands of potential voters the time they need to get state-approved identifications.

Municipal clerks responsible for administering elections — there are 1,800 in Wisconsin, more than any other state — are now asking people who have already cast their votes by absentee ballot to send in photocopies of their identifications before their ballots are counted.

Arkansas has asked the state Supreme Court to overturn a Pulaski County judge’s injunction against that state’s version of the law. The Pulaski County judge stayed his own ruling, in anticipation of a higher court’s review.

Voting rights groups are most concerned about North Carolina. There, a district court judge ruled in favor of the state’s 2013 voting law, which made changes to early and provisional voting procedures, among other alterations. This week, the 4th Circuit reversed that order, though the district judge has not officially reversed himself. The judge canceled a planned hearing Friday morning after North Carolina appealed to the Supreme Court, and voting rights groups filed an emergency petition seeking action from the 4th Circuit.

The burden of last-minute procedural changes falls on the shoulders of election administrators, most of whom are collecting absentee ballots.

“We have over 2,500 precincts in North Carolina. We have hundreds of early voting center sites. All of their precinct workers or poll workers or one-stop voting site workers have been trained,” said Susan Myrick, an elections policy analyst at the Civitas Institute, which supports the changes to North Carolina’s election law. “You have at least 10,000 people that have been trained in a certain way, and now you’re looking at a closing window. It is going to cause confusion. There’s no doubt.”

Hans von Spakovsky, a former federal election commissioner and manager of the Election Law Reform Initiative at The Heritage Foundation who supports voter identification laws, said the voting rights groups filing lawsuits are doing so because the courts are their only remaining avenue.

“What’s clearly going on there is they couldn’t convince the legislatures to change early voting days, so they go to court and they find a sympathetic judge,” von Spakovsky said. “Trying to change the rules this close to an election just causes nightmares for election officials.”

After the 2008 Supreme Court decision upholding Indiana’s identification law, and after the Republican wave of 2010 put so many legislative chambers in GOP control, both parties sought to use changes to election laws to their advantage.

“There’s a lot of activity going on right now because a lot of these elections are close, and I think that creates a temptation for people to monkey around with these things,” the ACLU’s Ho said.

Both voting rights advocates and voter identification supporters expect one or more cases to land in front of the Supreme Court either this term or next term, but certainly after the election. The court, experts said, is not inclined to take up a full case for review when it has been submitted for emergency action. But the delay doesn’t mean the cases aren’t important.

“These battles are in some ways more important for 2016 than for 2014, when the presidency will be on the line,” said Hasen. But, he warned, voting rights groups might not necessarily want to see an identification case come before the Supreme Court: “It’s not really a hospitable place to be these days if you’re a voting rights advocate,” he said.