In the final stretch before Election Day, ballots have been set on fire and damaged in two ballot drop boxes and a Postal Service mailbox in three states. Federal officials have warned that in recent months, some social media users have encouraged sabotage of ballot drop boxes.

Early on Monday morning in Oregon, Portland police responded to a fire they say was started by “an incendiary device” inside a ballot drop box. Oregon’s Multnomah County Elections Division said in a statement that three ballots were damaged. “Fire suppressant inside the ballot box protected virtually all ballots,” the statement read.

Hours later, another drop box was set on fire in nearby Vancouver, Washington, where officials say “hundreds” of ballots were badly damaged when that box’s fire suppression system failed to work.