Greenpeace executive Pascal Husting has been accused of hypocrisy after it emerged he flies 800 kilometres to work and back.
Since 2012, the environmentalist has avoided the 12-hour return train commute in favour of flying from Luxembourg to Amsterdam.
Husting, who is international program director at Greenpeace International, makes the journey twice a month at a cost of £215 to the charity.
But it is the cost to the environment that has riled campaigners, with Greenpeace supporters threatening to cancel donations after Husting's less-than green travel arrangements were leaked to the Guardian.
Greenpeace has campaigned to cut air travel and spoke out against "needless" domestic flights.
Greenpeace activist Richard Lancaster, who has a 30-year association with the group told the Telegraph: "I volunteer with Greenpeace but work in the commercial world and if I took a job in another country I'd expect to move to where the job is and, if I couldn't for family reasons, I wouldn't take the job — so I find Pascal's travel arrangements almost unbelievable."
According to airline KLM, each of Husting's trips would generate 142kg of carbon dioxide emissions, — a carbon footprint equivalent over one year of more than three flights from London to New York.
From September, Husting said he would be making the trip only once a month and by train.
In a statement, Husting said: "To be frank I'm embarrassed, it was a misjudgment, there's no doubt about it. It was meant to be a temporary arrangement so I could do the job and be with my family because my kids are so young, but that's not good enough. The job ended up lasting longer than I expected it would, but I should have been taking the train from day one. That's happening now."
Greenpeace boss John Saven wrote on his blog: "As for Pascal's air travel. Well it's a really tough one. Was it the right decision to allow him to use air travel to try to balance his job with the needs of his family for a while?
"For me, it feels like it gets to the heart of a really big question. What kind of compromises do you make in your efforts to try to make the world a better place?
"Honesty and integrity to the values that are at the heart of the good you're trying to do in the world cannot be allowed to slip away. For what it's worth, I don't think we've crossed that line."