More than 6 million Americans won’t be casting their ballots on Nov. 8 because of state laws restricting the voting rights of people with felony convictions.

The country’s disenfranchised population hit record levels this year, according to a report released earlier this month by the Sentencing Project, a nonprofit focusing on issues in the criminal justice system.

States have the authority to withhold voting rights from anyone with a criminal conviction, under the Fourteenth Amendment of the Constitution. How that authority is exercised, and whether ex-cons can apply for restoration of their rights, is left up to the states to decide.

As a result, the landscape of felon voting laws is constantly shifting and increasingly varies from state to state.

In 1976, approximately 1.17 million people were unable to vote due to felon disenfranchisement laws. In 1996, that figure was 3.34 million. Today it’s 6.1 million, thanks to booming prison populations and longer sentences.

One in every 40 adults is unable to vote because of a current or prior felony conviction. For African Americans, the rate is one in 13, the Sentencing Project found.

More than seven percent of voting age population are barred from participating in the political process in Alabama, Florida, Kentucky, Mississippi, Tennessee and Virginia.

Disenfranchisement among those with felony convictions has fallen disproportionately on black voters. In 2016, more than five percent of black adults were unable to vote in 23 states due to a criminal conviction. In Kentucky, Tennessee and Virginia, more than 20 percent of adult African Americans are unable to vote.

Critics of felon disenfranchisement laws say that they disproportionately exclude minority voters from the political process. A study led by sociologists at Northwestern University in 2003 found disenfranchisement policies likely impacted the outcomes of seven Senate races from 1970 and 1998 — and may have even swayed the close presidential race between George W Bush and Al Gore in 2000, particularly considering how hotly-contested Florida was, the state that has one of the highest disenfranchisement rates in the country.

Approximately 1.7 million Floridians, or more than 10 percent of the state’s voting age population, are disenfranchised because of a criminal conviction, according to research by the Brennan Center for Justice, a left-leaning public policy institute. More than 21 percent of the state’s black voting-age population are blocked from casting their vote.

A 2014 study led by political scientists from University of Pennsylvania argued that ex-felons were generally more likely to vote Democrat. Based on a predictive model that used demographic factors such as gender, race, age, income, labor force status and education, the authors concluded that 73 percent of the disenfranchised population who registered to vote would do so as Democrats.

Virginia Gov. Terry McAuliffe, who has been fighting to restore voting fight to felons who have completed their prison sentence in his state, has called felon disenfranchisement a vestige from Jim Crow laws. State Republicans accused McAuliffe, a Democrat, of political opportunism and pursuing the cause in the hopes of shoring up votes for his party.