Fundraising bodies that accept credit or debit card donations need to prepare for new regulations from MasterCard and Visa that could prove expensive.
The credit card giants are encouraging charities to capture the three-digit security code from the signature strip when accepting donations from cardholders.
The Institute of Fundraising, which originally thought the regulations were a mandate for charities as well as businesses, is concerned by a lack of clear guidance and the absence of consultation with charities.
But Paul Ravenscroft, a spokesman for Visa, said Visa had not mandated the changes but was making recommendations to improve safety for transactions when cardholders are not present.
He said: "Inevitably, these security improvements have repercussions, but Visa's first commitment is to protecting the integrity of the system and its participants."
Megan Pacey, director of policy and campaigns at the Institute of Fundraising, said: "It is clear that these changes will create significant challenges for many fundraisers."
She said one of the biggest difficulties will be the need to destroy security codes after transactions while also keeping Gift Aid declarations, which are often included on the same form.