United Parcel Service and FedEx on Friday shot down social media calls that they step in to deliver mail-in ballots from the U.S. Postal Service, 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 in a statement.

“FedEx does accept individual ballots, and we advise that customers planning to return their ballots via FedEx should closely review their state’s guidelines on absentee voting and deadlines for ballots or related election documents,” FedEx said.