Greenpeace has been warned against encouraging anti-social behaviour after an ad asked supporters to sponsor the painting of a power station chimney.
The organisation's sponsorship page said in December: "Chimneys, they're a bit dull aren't they? We prefer them when they have statements written down them, like 'no new coal' or 'stupid', which say what we think about them."
It asked supporters to donate money to pay for Greenpeace to paint a chimney and used an example of activists painting the Kingsnorth power station in Kent.
An internet user complained that the appeal was harmful and irresponsible because he believed it encouraged consumers to sponsor an illegal activity and encouraged and condoned anti-social behaviour.
Defending the ad, Greenpeace said it took non-violent direct action based on the intention to protect the planet from environmental harm and did not aim to break the law, adding that the Kingsnorth activists were found not guilty of criminal damage.
It said its actions came from deeply held values, which it believed were for the good of society, and therefore refuted the allegation that it would do anything anti-social.
Upholding the complaint, the Advertising Standards Authority said that although the Kingsnorth activists had been found not guilty of criminal damage, similar activity might lead to acts that were illegal or anti-social.
It said: "Although we considered that the claims themselves were unlikely to influence the public to engage in such exploits themselves, we considered that the claim '£80 Send this Gift. How this gift works' sought donations in order to make it possible to finance similar direct action by others and thereby encouraged such behaviour.
"We therefore concluded that the ad was harmful and irresponsible because it encouraged and condoned anti-social behaviour."
It ruled that the ads must not appear again in their present form and told Greenpeace to ensure that their advertising did not encourage or condone anti-social behaviour.