Among its changes, the bill would require everyone registering to vote or updating their registration information to present documentary proof of citizenship in person. Recent studies have shown that millions of eligible voters lack easy access to documents that prove their citizenship, like a passport, birth certificate or naturalization papers.

As many as 21.3 million U.S. citizens — more than 9% of voters — do not have such documents readily available, and over 3.8 million people — around 2% of voters — don’t have any form of proof, according to recent survey results gathered by the Brennan Center for Justice and other organizations.

The law would disproportionately affect voters of color. Millions of people who have taken their spouse’s last name — which includes approximately 69 million married women — and people who have changed their names may also face difficulty when registering or updating registration info because the law doesn’t specify what documents would be accepted to prove their identity.

Rural voters or people with disabilities would be affected as well, because the measure requires documents to be presented in person, which also undermines mail and online registration systems and voter registration drives.

“My Republican colleagues crafted and passed one of the most damaging voter suppression bills in modern history,” Rep. Joe Morelle (D-N.Y.) said in a statement. “There’s no doubt that women, military members, and people of color will be disproportionately impacted. The fight to stop this bill – to protect Americans’ sacred right to vote – is not over.”

In addition to its citizenship requirement, the SAVE Act threatens election workers with up to five years in prison or civil lawsuits if they register someone without the correct documents, even if that person is a citizen.

and the bill aims to restrict mail voting by barring states from counting mail ballots that arrive after Election Day, as many states currently do.