United Parcel Service (UPS) and FedEx on Friday shot down social media calls that they step in to deliver mail-in ballots from the US Postal Service (USPS), which is warning states of potentially "significant" delays.

"State ballots must be postmarked to be considered valid and only the USPS has lawful postmarking status. Therefore UPS, FedEx, and other private parties cannot technically be involved in shipping ballots," UPS told Reuters in a statement.

"FedEx does accept individual ballots, and we advise that...