Think you know your state’s voting rules? Better check again before heading to the polls next month.

Depending on where you live, those rules might have changed since the last time you voted. And those changes could affect outcomes in a number of tightly contested congressional races that will determine which party controls the U.S. Senate.

22 states have enacted new voting restrictions since the 2010 election, according to the the Brennan Center for Justice, a nonprofit law and policy institute that advocates for more inclusive voting policies. This November marks the first time the majority of those new laws will be in place, resulting is an ever-shifting landscape of wildly inconsistent and often confusing election laws.

Brennan Center for Justice (click image to access interactive map)

Passed mainly in Republican-led state legislatures, with the stated intention of reducing voter fraud, the new laws range from photo ID requirements and early voting cutbacks to registration restrictions and voting rights limitations for ex-felons.

Voter identification requirements remain the most controversial of these laws. Because certain kinds of ID, particularly photo IDs, often require administrative fees to procure (like a drivers’ license), opponents claim the laws is tantamount to a poll tax. Laws in 34 states require voters to show some form of identification at the polls, and as of mid-October, 31 of these laws were in force, according to the National Conference of State Legislatures.

National Conference of State Legislatures (click image to access interactive map)

Opponents argue that stricter voting laws disproportionately suppress turnout among students, African-Americans and low-income voters, groups that tend to vote democratic. They point to numerous non-partisan studies showing that voter fraud is exceptionally rare and statistically insignificant. In one 2012 analysis — which advocates of stricter voting laws were quickly dismissed – the student reporting agency News21 looked at more than 2,000 cases of alleged voter fraud around the country that have reported since the 2000 election. Of these, it found only 10 actual instances of voter impersonation, the equivalent of roughly one case for every 15 million voters.

There’s less evidence, however, about how much restrictive voting laws actually suppress turnout on Election Day.  But while the specific impact is unclear, Democrats fear that even a 1 or 2 percent decline in participation among registered voters in tightly contested congressional and gubernatorial races could be enough to sway the outcome.

The Brennan Center characterizes the recent slate of new voter restriction laws as the most widespread effort to restrict access to the polls since the passage of racist Jim Crow laws adopted throughout the South in the decades after Reconstruction. It’s an effort that’s intensified since 2013 Supreme Court ruling weakening the 1965 Voting Rights Act by allowing jurisdictions with a history of voter suppression to enact new voting laws without seeking approval from the federal government.

And then there are those last minute changes …

Furthering the confusion, seven of the newly enacted state laws have been challenged in court by voting advocates, charging that the new rules discriminate against certain groups of voters. And with just weeks before election day, a cascade of recent court rulings have led to last minute changes in statewide voter rules, causing panic among election officials, and potentially affecting the outcomes of races.

Last week, the U.S. Supreme Court upheld an Ohio law that cut early voting in the state by one week. But in a separate ruling the court blocked Wisconsin from implementing its 2011 photo ID law on the grounds that there wasn’t enough time for it to be implemented before the general election.

Meanwhile, on October 14 a federal appeals court temporarily reinstated Texas’ strict photo voter ID law after it had been struck down a week earlier by a lower court. And just days before the start of early voting in Arkansas, that state’s highest court struck down a law requiring voters to show photo ID.

Brennan Center for Justice (click for interactive version)

No precedent in the Constitution

“It’s really not one America when it comes to voting,” Judith Brown-Dianis of the Advancement Project explains in the recent documentary Electoral Dysfunction.

In fact, the text of the original Constitution doesn’t actually include a single mention of voting rights; the founders left this to the discretion of the states. Only subsequent amendments (namely, the 15th, 19th, 23rd and 26th) prevent voting rights from being denied to certain formerly disenfranchised populations (people of color, women, 18 to 20 year olds). As long as states adhere to those rules, they are largely free to determine their own voting laws.

“The Constitution, at the nation’s birth, made no mention of voting rights whatsoever,”  Harvard University History Professor Alex Keyssar notes in the  documentary. “[The Founders] were unsure, in fact, whether voting was a right or a privilege. And if it was a right, they weren’t sure who the right actually belonged to.”

The ambiguity continues to play out today. It’s why in a conservative state like Alabama, voters are strictly required to show photo ID, and anyone who’s ever committed a felony permanently loses the right to vote, whereas in a liberal state like Vermont no identification is required, and even prisoners can cast ballots.

Additional resources

Links to official election resources for all 50 states

Brennan Center: state-by-state student voting guide

ProPublica: Everything that’s happened since the Supreme Court’s Voting Rights Act decision