A midsummer fee increase for immigration paperwork prompted millions of people to apply for naturalization and other immigration benefits before the fees changed.

But now those forms are piling up, and service centers in Nebraska and Texas have the longest delays.

The paperwork problems could keep some immigrants from becoming U.S. citizens in time to vote in next November's presidential election.

The application backlog is so large that Citizenship and Immigration Services, a division of the Homeland Security Department, is months behind schedule in returning receipts for checks written to cover fees. And that's an early step in the process.

Agency spokesman Chris Bentley says at least 110 immigration workers have volunteered to help process applications and are being sent to Texas and Nebraska.