The U.S. Postal Service has issued guidance to voters casting their ballots by mail ahead of the general election on November 5.

Election officials have raised concerns about the U.S. Postal Service’s ability to deliver mail-in voting ballots by state deadlines. The Postal Service says it’s taking “extraordinary measures” to ensure successful operations.

Roughly a fifth of voters are expected to vote by mail in the 2024 election, according to recent polls, meaning millions of ballots will be in the hands of postal workers.