SAN FRANCISCO (CBS SF) – Voting by mail begins Monday for California’s June 5 primary election. But for one group of voters, its looking likely that many ballots won’t count.

When you vote by mail, you have to put your signature on the envelope that contains the ballot, and it has to resemble what you’ve put on your voter registration card.

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“It doesn’t have to match, it doesn’t have to be letter for letter but you have to be able to look and say yep, that’s the same person,” explained Contra Costa County Clerk Stephen Weir.

He warns of an alarming trend among young voters, specifically in the 20 to 29 age group, having their ballots rejected because of signature irregularities. That age range made up just 6% of Contra Costa County’s voting population in 2010 but accounted for 30% of the rejections, leading some to speculate that other members of the household are signing the ballots.

“Which of course isn’t legal,” Weir warned.

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He hopes it’s something less sinister, though.

“I think that the younger folks have not perfected their signature,” he theorized.

Whatever the route of the problem, he says it pains him to see the ballots of the least-frequent voting population being tossed out.

KCBS’ Janice Wright Reports:

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