It's because of a recent change in how the United States Postal Service processes mail. Mail at post offices and USPS collection boxes located 50 miles away from a regional hub is now picked up the next day.
According to officials, that means mail-in ballots dropped off on Election Day, June 2, will not be postmarked until the following day. Ballots must be postmarked by June 2 in order to be eligible for counting.
If you miss Tuesday's recommended deadline, you have a few options.
You can drop your ballot off at a voting center or ballot box, or you can go to a post office to request a postmark on your ballot.
There are two big races to watch in this election - the race for Los Angeles mayor and California governor.
If you're voting in person, you'll have until 8 p.m. on Election Day. If you haven't registered to vote, you can do same-day registration at your local voting center.