Mexico City, Jan 23 (IANS/EFE): The tool of their trade is a flannel rag and their office is the street. They are the windshield cleaners, and their livelihood is now threatened by parking meters.

More than four million vehicles are on the road every day in Mexico City, one of the biggest, most densely populated cities in the world, where finding a parking place can be a daily headache.

Parking is costly and complicated in the Mexican capital, first because of the want of space, and secondly because the streets are "owned" by the windshield cleaners, who charge a voluntary or set fee for parking a car or just for watching to see that nothing happens to it.

"I leave my car at the entrance to my office, he parks it and brings it to me when I'm ready to leave, all for 30 pesos ($2.30) a day," Carlos Perez, a customer of this informal service who doesn't worry about leaving the keys to his car every day with someone he hardly knows, told EFE.

It's the price one has to pay to avoid driving around the block a thousand times to find an empty parking place, something almost impossible in certain districts of the Mexican capital taken over by windshield cleaners like Hugo Diaz, 32, who after 10 years in the business says he works "from dawn to dusk" to put food on the table for his family.

He earns some 200 pesos ($15.70) a day for watching cars in his area and he doesn't know what kind of work he'll do when the parking meters start functioning that authorities in his area recently had installed.

In Mexico City, according to estimates of the Federal District Labor Secretariat, there are some 22,000 windshield cleaners.

Of those, a total of 6,849 are registered, though not legalized, since they pay no taxes nor do they receive any welfare benefits.