The San Luis Obispo County Clerk-Recorder's office says the county's ballot printer and mailhouse vendor inadvertently sent two identical vote-by-mail ballots to 2,666 voters.
These voters should be receiving postcards informing them of the duplicate ballot and what they should do with it.
Voters are asked to vote using only one ballot and discard the other.
The Clerk-Recorder's office says that if the Elections Department receives duplicate ballots from the same person, the system will flag it and only one ballot will be counted per voter.
In a statement released Friday, County Clerk-Recorder Tommy Gong said, "While it is unfortunate that some duplicate VBM ballots were sent to voters, we were able to quickly discover the discrepancy and develop a plan to notify affected voters of the situation and how to rectify it. We regret ay confusion and inconvenience this has caused."