Georgia’s Republican-controlled state election board voted on Friday to require a labor-intensive hand count of potentially millions of ballots in November’s election, a move voting rights advocates say could cause delays, introduce errors and lay the groundwork for spurious election challenges.

The hand count rule, passed in a 3-2 vote, will make Georgia the only state in the U.S. to implement such a requirement as part of the normal process of tabulating results, according to Gowri Ramachandran, the director of elections and security at New York University’s Brennan Center for Justice, a left-leaning public policy institute.