Pierrette Rey was speaking at a summit of the International Civil Aviation Organization (ICAO) in Montreal, Canada, where representatives of 191 countries gathered to agree an initiative aimed at controlling emissions and carbon offsetting in the airline industry.
So far 63 countries have opted to join the plan, WWF said.
But according to Rey, WWF fears the voluntary agreement won't do enough to protect the environment and a better solution would be to cut down the number of flights, newspaper Le Matin reported on Friday.
And Switzerland is particularly guilty of excessive use of flying, she feels.
“The Swiss take the plane twice as much as their neighbours. We must reduce the number of flights,” said Rey, stressing the efficiency of train services in Europe.
To encourage people to cut down on flying, an additional tax should be applied to plane tickets under the ‘polluter pays' principle.
The money gained would then be given back to the non-flying population.
“It would increase awareness among those who fly and compensate those who never do,” Le Matin reported Rey as saying.
According to ICAO figures, Swiss-registered airlines carried 27 million passengers in 2015. That compares with 15 million in Austria, a country of a similar population size.
Bigger neighbours France and Germany carried 65 million and 116 million respectively.
Switzerland has good train connections across Europe, with Milan and Paris only a few hours journey by rail.
A Swiss team recently successfully flew around the world entirely on solar power.
Bertrand Piccard, one of two pilots who shared the 42,000km journey in Solar Impulse 2, hailed the plane as the "future" for the aviation industry.
But commercial solar-powered planes remain a long way off.