Celebrities including Demi Moore and Emma Stone were among thousands of people who mistakenly registered as members of an ultra-conservative political party, an investigation has found.
The American Independent Party (AIP) - which opposes abortion rights, same sex marriage and has called for a fence to be built around the Unite States border - has nearly half a million registered supporters.
But a poll of 500 members in California conducted for the Los Angeles Times discovered nearly three quarters (73%) did not realise they had joined the party.
Voters were confused by the use of the word "independent" in the party's name and many believed they were declaring they had no political affiliation on their voter registration form, the newspaper reported.
The mistake could cause problems for people wanting to vote in the US presidential primary election in California on June 7, as voters affiliated with the AIP would only be allowed to vote for candidates on the party's ballot, it added.
The LA Times obtained a list of all people in the state registered with the AIP, which included the names of Demi, Emma, former boxer Sugar Ray Leonard and The Big Bang Theory star Kaley Cuoco.
In a statement to the paper, Kaley said: "The views of this party do not accurately reflect my personal beliefs and I am not affiliated with any political party. As such, I am taking the necessary steps to immediately remove my name as a member of this voting party."
A spokesman for Demi, who has previously campaigned for President Barack Obama, said she had never been a member of the party and any record stating otherwise was a "mistake".
Emma and Sugar Ray plan to re-register before the June election, representatives told the LA Times.