CBS Local — It’s the busiest time of the year for package delivery companies and officials say that there are some major concerns for people expecting shipments before the holidays.

The FBI is warning Americans to watch out for fake emails claiming to be from FedEx, UPS, and the U.S. Postal Service which are really filled with viruses. The scam reportedly tells customers, many who may be waiting for holiday packages, that their shipment could not be delivered. The notice then instructs victims to click on a phony link to receive an invoice number for their package.

The FBI is telling people to delete any suspicious emails about package deliveries and is directing anyone who receives the notices to file a complaint with their Internet Crime Center.

The news for actual deliveries is equally grim, according to UPS. The international delivery service says it is already falling behind schedule this year, despite investing in new warehouses and seasonal employees for the holiday rush. A Dec. 6 notice from UPS says the company is working on several plans to make sure the bulk of packages arrive at their destinations on time.

“Amazon is already expecting delay problems — we know this from UPS and certainly from our own flight problems — and we’re expecting that it’s going to get worse in the next two weeks leading up to Christmas,” Robert Kirchner of Atlas Air Worldwide Holdings told The Washington Post. Shoppers are already expressing their frustrations on social media with long shipping delays.

For holiday gifts being shipped by regular ground service, FedEx is advising customers to ship their gifts no later than Dec. 15 for delivery by Christmas. The U.S. Postal Service is giving their customers until Dec. 14 for Christmas arrivals.