With the midterm elections two months away, a federal whistleblower has warned that the U.S. Postal Service’s new mail voting system is untested, fatally flawed and likely to lead to a “catastrophic failure” if it’s implemented ahead of November’s midterm elections. Critics warn the system could disenfranchise millions of voters.

In March, President Trump signed an executive order directing his administration to create federal lists of citizens and directing the Postal Service to refuse delivery of mail-in ballots to people not on those lists. Voting rights groups and state officials have sued to block the new rules.