When Jim Allen, the elections director for Delaware County, Pennsylvania, recently ran a training session for poll workers, he began a conversation about a topic he’d never previously had to address during training: prediction markets. “There was one person who stood up, and they said, ‘Well, what if we just want to make a minor bet on what turnout will be, that’ll keep things interesting?’ And we said: ‘No, this is all bad,’” Allen, who oversees 383 precincts, recounts.

As a result, Allen and the board of elections in Delaware County amended the oaths signed by people involved in elections to include “an affirmation that the workers have no direct or indirect interests in any bets, wagers, or prediction markets.”

Some 2,500 people, including everyone from full-time staff in the elections office to temporary employees helping process ballots on Election Day, have signed the oath ahead of November’s midterms.

“The rapid growth of prediction markets, and their plans to prey on elections, are direct threats to undermining trust in electoral outcomes,” Allen tells WIRED. “The overriding concern is that prediction markets have the potential to monetize a reward for manipulating results and, equally concerning, capitalizing on the anger and frustration by those who lose in these prediction markets.”