As Bernie Sanders and Hillary Clinton prepare to face off in New York on April 19, voters are speaking out against the state’s egregious rules that they say favor Clinton and disenfranchise would-be voters.

Two crucial dates for New Yorkers have already come and gone: the October 9 cutoff to change party affiliation and the March 25 deadline to register as a voter. Because the state runs “closed” primaries—which only allows registered Democrats to cast a ballot—voters who weren’t aware of the dates will be left out of the process.

For Sanders, who scores high among independents but splits Democrats about evenly with Clinton, the party requirement could be his “Achilles’ heel,” as MSNBC political reporter Alex Seitz-Wald puts it.

According to Board of Elections data, about 20 percent of the state’s 11.7 million voters are unaffiliated with any party, Seitz-Wald writes. Among those barred from casting a ballot next Tuesday are those registered with the Working Families Party, a center-left political party with 48,000 voters, that recently endorsed the Vermont senator.

Voters say that for those who support Sanders—many of whom are first-timers who may not have been aware of the deadlines, and others who didn’t catch Bernie fever until he became a serious challenger—the rules amount to disenfranchisement.

“I actually mailed in my registration the moment I felt convinced, which I think was mid-November,” a Brooklyn-based political organizer, Kayla Santosuosso, told the Guardian on Tuesday. She only realized she was still unregistered after checking her information on the Board of Elections website six months later.

She wrote on her blog at the time:

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