Nearly half a million California voters may be unable to participate in the state’s presidential primaries on June 7 as a result of confusion in the voter registration process, a Los Angeles Times investigation has discovered.

Hundreds of thousands of Californians who intended to register as independents may have accidentally registered instead with the ultra-conservative American Independent Party (AIP), which opposes abortion rights and same-sex marriage, and calls for building a fence along the entire U.S. border.

The LA Times reports that “a majority of (AIP) members have registered with the party in error,” and that “nearly 3-in-4 people did not realize they had joined the party” after surveying registered members.

The Times had a team of Republican and Democratic pollsters contact a list of 500 AIP members, obtained through a public records request, who determined that “fewer than 4% could correctly identify their own registration as a member of the American Independent Party.”