MADISON, Wis. — Hundreds of absentee ballots in Wisconsin's April primary election never made it to voters or went uncounted because of postmark problems, the U.S. Postal Service has reported.

The Postal Service's internal watchdog found hundreds of ballots went undelivered due to election officials attempting to send absentee ballots to voters at the last minute, inconsistent postmarking and one mail carrier erroneously delivering outgoing absentee ballots back to the election office, the Milwaukee Journal Sentinel reported.

The election, which decided races for the Wisconsin Supreme Court and the presidential primary, was carried out amid the coronavirus pandemic after a push by Republicans to forge ahead with voting. It was marked by chaos as nearly 1 million people cast mail-in ballots. Many voters complained that they had requested absentee ballots that never arrived, forcing them to choose between sitting out the election or risking infection by voting in person.

Completed absentee ballots had to be filled out and postmarked by election day in order to be counted. The cut-off date for ballots to be delivered to clerks was April 13.

The Wisconsin election crystallized what's expected to be a state-by-state legal fight over how citizens cast their ballots if the coronavirus outbreak persists into the November election.