Police are investigating after people living in Bispham and Wesham, reported receiving a large number of bags claiming to be from the North West Air Ambulance.
However, the charity has said it is not currently delivering in the area.
The Fundraising Standards Board (FRSB), the independent regulator, said it had not been made aware of the reports but was keen to investigate further.
A spokesman said: “The public should be reassured that the large majority of collections are genuine, but that there are some simple checks they can make if they have concerns.”
Anyone concerned about the authenticity of a collection bag is advised to contact the charity directly to see if they are collecting.
The North West Air Ambulance said donations can be made directly at its stores or a collection can be arranged online or by phone.
Jenny Haskey, head of fund-raising at the North West Air Ambulance, said: “We aren’t currently posting recycling bags to homes.
“If you do receive a recycling bag, please do make us aware by emailing [email protected] with your name, contact details and a photo of the bag if possible.”
Tips for donating safely and contact details are available on the FRSB website: www.frsb.org.uk