Simon Wong, a paramedic for West Midlands Ambulance Service, said some of his colleagues returned to their vehicle after the emergency call in Erdington, Birmingham, to find the rude note on the car.
It read: “Nice one blocking road.”
The note was dated Monday and was written on a UPS delivery slip, usually left when a driver has not been able to deliver a parcel.
Sharing it on Twitter, Mr Wong wrote: “A Colleague returned to [ambulance] yesterday PM during a 999 call in Erdington to find this note on their [ambulance] by a @UPS_UK @UPS driver.
“Crew had parked on a verge, where vehicles were still passing ok. Unfortunately whilst treating a pt, other road users parked opp [ambulance] blocking the road.”
Although the note was left on UPS paper, it is not clear whether its author works for UPS.
The note comes three months after Kirsty Sharman was fined £120 for leaving an abusive note telling staff they had “no right” to park an ambulance outside her home in Stoke-on-Trent.
A West Midlands Ambulance Service spokesman said: “Finding another note like this is very disappointing. We are all busy people, so our staff will never block a road unless absolutely necessary, where a patient’s life could be at risk.
“In this case, it would appear that the crew had parked appropriately when they arrived, but the situation had developed while they were with the patient.”
A UPS spokesman told Sky News: “We are investigating the issue and appropriate actions will be taken to ensure our drivers are aware that any such behaviour will not be tolerated. UPS values treating others with respect and understanding at all times.”