Supervisors Janice Hahn and Sheila Kuehl proposed the change to election protocols that typically send vote-by-mail ballots on request.
"It is hard to imagine that, amid the coronavirus crisis, we have a major election coming up this November,'' Hahn said. "We don't know what challenges we will be facing in this pandemic this fall, but by sending every voter a mail-in-ballot we can ensure that everyone can cast their ballot safely, no matter what the future holds.''
In a statement, Kathay Feng, executive director of California Common Cause, applauded the decision to expand voting options.
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"In America, voters shouldn't have to choose between their health and exercising their right to vote," Feng said.
The countywide "safer-at-home" order that was prompted by the coronavirus crisis is currently schedule to expire on May 15, although physical distancing is likely to be necessary beyond that date.
President Donald Trump has previously criticized vote-by-mail balloting, which he described as "a terrible thing."
Trump himself voted by mail in the most recent election.