Air ambulance officials say they will have to stop doing night flights to save money and because its medics are needed in hospitals.
The Lincolnshire and Nottinghamshire Air Ambulance has already started scaling back night operations.
But from the start of May it will not cover night flights because some medics are needed to deal with coronavirus.
The charity said the loss of funding events and closure of its shops would see a shortfall of £3m in funding.
Now officials at the air ambulance are asking for help to fund the service.
The charity said in a statement: "We have already had to scale back night missions meaning our helicopter will not be making night missions at all as of May.
"This move is due to some of our crew being called back to support the NHS, while some are self-isolating, unable to travel or have become ill.
"The initial impact of coronavirus left us no other option than to cancel our fundraising activities and close our shops.
"We anticipate we may lose up to £3m in income as a result."
On Wednesday, Chancellor Rishi Sunak announced a £750m package to keep struggling charities afloat during the coronavirus pandemic.
Chief executive Karen Jobling said: "We continue to carry out life-saving missions every day but, along with a reducing service, we are concerned about the impact of this significant income drop when we are able to resume our service.
"We need to be safeguarded against these effects so that we can continue our missions now and return to full capacity, while realising our ambition to be a full 24/7 service."