Pennsylvania, a key swing state, is dealing with a number of challenges during an unprecedented election – including postmarking mail-in ballots, which could be critical as a means to prove votes were cast on time.

In Pennsylvania, postage is prepaid on ballot envelopes to be returned by mail. Typically these prepaid envelopes are not automatically postmarked.

In a statement to Fox News, a spokesperson for the Postal Service said that the agency will “try to ensure” that every ballot mailed by voters receives a postmark, whether it is prepaid or mailed with a stamp by voters.

“Although we instruct our employees throughout the country to adhere to our ballot postmarking policy, such practice does deviate from normal procedures, since the primary purpose of cancellation is to ensure that postage cannot be reused, and some categories of postage are pre-canceled before they enter the mailstream,” the spokesperson said. “As a result, we acknowledge that circumstances can arise that prevent ballots from receiving a legible postmark.”

A postmark could be particularly important in Pennsylvania after the Supreme Court ruled that ballots received by Friday, Nov. 6 can be counted, so long as they are postmarked by Election Day.

PENNSYLVANIA'S MAIL-IN BALLOT PLANS VARY; SOME COUNTIES TO START COUNTING AFTER ELECTION DAY

A spokesperson for the Pennsylvania Secretary of State said that in this specific scenario, it will be presumed that ballots were postmarked by Election Day absent evidence that indicates otherwise.

“Under the Pennsylvania Supreme Court ruling that allows the three-day extension, ballots with no postmark or an illegible postmark are presumed to have been postmarked by the Election Day deadline, unless there is evidence the ballot was mailed after the deadline,” the spokesperson said.

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Many people who registered to vote by mail have already done so. However, as of Thursday, about 1 million mail-in ballots had not been returned, as reported by The Associated Press.

Pennsylvania is anticipating a record volume of mail-in and absentee ballots for the November general election. Around 2.5 million people are expected to vote by mail.

Despite the expected surge in mail-in ballot volume, Pennsylvania is one of a handful of states where the ballot counting process, including pre-canvassing (sorting, verification and other processes that precede actually counting the vote) cannot begin before Election Day.