Charities are concerned about what new EU cookie laws will mean in practice and how they should comply.
From 26 May, all website operators must gain the consent of web users before putting cookies on their computer systems.
The rule stems from an EU directive that was passed in May last year, but UK operators were given a year’s grace to comply.
A cookie is a simple text file that gets downloaded onto your computer when you visit a website. There are different types of cookies, including ‘analytic’ files that track visitor numbers and the popularity of pages. Some cookies allow organisations to target advertising at users through their own and other websites.
The rules mean that users will have to opt in to receive all ‘non-essential’ cookies. This includes those used to recognise users for analytical and advertising purposeswhen they return to a website.
John Brunsdon, director of the marketing and web agency Tickbox, warned that the new rules might mean "big problems" for charities, because people would be put off using charity websites and making online donations if they had to give consent to cookies.
He said there was uncertainty among charities over how the new rules would be enforced by the Information Commissioner’s Office.
"A lot of clients are asking about it and saying they are worried," said Brunsdon. "I cannot say 'ignore it'. A lot of people are waiting to see what happens." The rules might also affect how charities measure the success of online campaigns, he said.
Erica Crump, an associate at the law firm Bates, Wells & Braithwaite, said: "Some organisations fear that asking users to consent to cookies when they arrive at a website could cause the number of visitors and donations to fall significantly."
A spokeswoman for Macmillan Cancer Support said: "Macmillan, along with all digitally enabled organisations, is concerned how the cookie legislation might impact on the customers’ experience.
"The benefits many types of cookie give to the user can be complex to explain to the average web user.
"We use them in various ways to ensure people living with cancer get the most optimised digital experience to support their journey, and so we will be working with our agencies and industry colleagues on options on how best to do this."
Olly Benson, head of projects at the online charity YouthNet, said the charity’s website used analytic cookies.
"Essentially we use Google Analytics, which is vital for us to be able to track and provide details of our usage. The ICO has said that they see things like analytics as low-priority in terms of taking action," he said.
"Once there is greater clarity on how the ICO is going to interpret the directive, we’ll review our position and make appropriate adjustments."
Michael Docherty, head of digital at Cancer Research UK, said the charity would carry out a "cookie audit".
"We have been exploring practical options to draw the public's attention to information about what cookies we serve, how we use them and how the public can opt out," he said.
A spokeswoman for the ICO said its approach to enforcement would be proportionate when taking into account the impact a cookie has on the privacy rights of a UK consumer.
"We will expect organisations to be on the path towards compliance," she said.