Secure ballot drop-off locations opened across the state on Tuesday.
"Democracy only works if people are free to vote without fear, without intimidation, without interference," Bonta said.
California voters have several options when it comes to casting a ballot, including voting in person at a voting center, dropping off a mail-in ballot at an official drop-off location or voting by mail.
Bonta's reminder comes as a case before the U.S. Supreme Court could invalidate ballots received after Election Day. It's unclear when the court could issue its ruling.
"With changes to postal delivery times, how you return your ballot matters," said Bonta. "This is why we're encouraging folks to vote early. Mailing your ballot on Election Day, or even one to two days before, could mean it arrives too late. You want your vote to be counted. I want your vote to be counted."
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Bonta also addressed speculation that federal law enforcement could be deployed to voting centers, warning that any effort to intimidate voters would be unlawful.
"Using immigration enforcement, real or implied, as a tool to scare people away from voting is illegal. Any presence intended to intimidate voters or suppress participation won't be tolerated," he said.
Secretary of State Shirley Weber also spoke about disinformation circulating online, saying false claims about ballot security have caused unnecessary concern among voters.
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"Some of you remember the rumor that went about people having holes in the ballot so people can peek through the envelope. And as a result of that, they could see how you voted. That is totally incorrect," Weber said.
For voters who are worried about mailing in their ballots, state and county officials say ballots can be returned at official drop-off locations.
In Los Angeles County, some early voting centers will open on May 23. All early voting centers are scheduled to be open by May 30.
The primary election is on June 2. The last day to register to vote in the primary election is May 18.