By Richard Galpin BBC correspondent in Athens, Greece

The union representing taxi drivers has condemned the practice

At the height of summer when the temperature in the Greek capital is usually well above 30C, it is unbearable to sit in a taxi without air conditioning.

The combination of heat, pollution, and slow moving traffic makes it almost impossible to wind down the windows to cool off.

This year, Athens taxi drivers have been taking advantage - charging passengers extra money each time they switch on the air conditioning.

It has become a common phenomenon.

So much so that the union representing taxi drivers in Athens has condemned the practice.

Reputation for rudeness

I have experienced it myself.

For example, the fare for a journey which I took last week in central Athens should have been two euros according to the meter.

But the driver demanded four euros to include the extra cost of running the air conditioning for approximately 10 minutes.

He became extremely irate when I questioned the legality of doubling the fare.

Athens taxi drivers already have a well-deserved reputation for rudeness and fleecing unsuspecting passengers, especially foreigners.

And even though there are 14,000 taxis operating in the city, it is often very difficult to get one to stop.