Donald Trump threatened on Sunday to withhold his signature from all bills until Congress passes a GOP-led voting bill that implements voter restrictions ahead of the November midterms.

“I, as President, will not sign other Bills until this is passed, AND NOT THE WATERED DOWN VERSION – GO FOR THE GOLD: MUST SHOW VOTER I.D. & PROOF OF CITIZENSHIP: NO MAIL-IN BALLOTS EXCEPT FOR MILITARY – ILLNESS, DISABILITY, TRAVEL,” Trump posted on his social media platform, Truth Social.

The bill, called the Safeguard American Voter Eligibility Act, or SAVE America Act, requires individuals to show citizenship documents to register to vote and strict forms of photo ID to cast a ballot. If passed, the legislation would also administer criminal penalties for election officials who register anyone lacking the required documents.

As my colleague Ari Berman wrote in February, the bill would potentially block tens of millions of Americans from voting. Nine percent of American citizens, or approximately 21 million people, don’t have ready access to citizenship documents. The bill may impact millions of US citizens in other ways: tens of millions of women who took their partner’s last name, for example, may not have a birth certificate that matches their legal name could find it more difficult to register.