COLUMBUS, Ohio (WCMH) — Four people are under investigation for potential voter fraud, accused of voting in Ohio and casting an additional ballot in a different state.

Ohio Secretary of State Frank LaRose announced in a letter on Wednesday four people have been referred to Ohio Attorney General Dave Yost and county prosecutors for potential voter fraud violations. LaRose said in a release the possible fraud occurred during the 2020 general election.

“Voter fraud is exceedingly rare in Ohio,” LaRose said.

In Ohio, 5.7 million people voted in the 2020 election with more than 3 million Ohioans voting for former President Trump and 2.6 million voting for President Biden.

The announcement is part of a partnership between LaRose’s office and several states that identify people who voted in one state and cast an additional ballot in Ohio. This round of referrals include individuals identified in Iowa, Missouri, Nevada and Oregon.

To verify the potential violations, Ohio and the partnering states cross-matched its voter history. Each case was then investigated in coordination with the secretary of state’s office or local jurisdiction in the additional state.

LaRose’s office said additional referrals with other partner states are expected.