All voters are required to hold a state-issued photo ID but it is estimated that one in 10 Americans does not have the necessary document.
When Barack Obama became the US's first black President he was elected with the help of the country's African Americans who turned out in big numbers to vote for him.
Their failure to back Hilary Clinton two years ago helped Donald Trump take the White House.
So the "Black vote" will be closely watched in the mid-term elections.
But in some states, African-Americans complain that they are being prevented from voting because of controversial voter identification laws.
All voters are required to hold a state-issued photo ID, which campaigners say has disenfranchised underprivileged African Americans.
It is estimated that one in 10 Americans does not have a necessary photo ID to vote.
"There are rural areas where a lot of people don't have drivers licences. A lot of adults don't have licences. They're very cheap but they're too expensive for them," says Scott Douglas from the Greater Birmingham Ministries.
TRT World's North America Correspondent Jon Brain reports from Selma, Alabama.