Mr Giuliani said that 100 undercover black police officers would begin hailing cabs, and drivers who did not stop might have their licenses suspended or their vehicles confiscated.

The sting "Operation Refusal" follows a formal complaint by black Hollywood star Danny Glover that New York taxi drivers had failed to pick him up because of his colour.

Mr Giuliani is thought likely to run for Senate next year

Mayor Giuliani said that cab owners and drivers would have to adjust to "the reality that life is going to be different now".

"There is going to be an intense effort starting on Friday to catch and to summons any taxi driver that refuses to take people to the destination that they request, whether that is a designation-based or a race-based refusal," he said.

"I think everybody who lives in this city knows that this has been going on for a very, very long time and maybe this is an opportunity to change it."

Glover complaint

Mayor Giuliani acknowledged that the discrimination suit filed by Mr Glover against the city's Taxi and Limousine Commission had prompted the campaign.

The Lethal Weapon star, who lives in San Francisco but visits New York regularly, alleged that five taxi drivers had bypassed him in Harlem one day in October.

Mr Glover's complaint sparked the crackdown

He said he was hightlighting a common complaint by black people that they often have trouble hailing taxis, even though the cabs are unoccupied and on duty.

"It happens to countless people every single day," he said. "The fact that I am a celebrity, the fact that I am visible allows me to draw attention to the issue."

The city requires a one-day cultural diversity seminar for cab drivers and has tried for years to weed out discrimination using undercover inspectors.

Officials said about 400 taxi drivers are cited each year for discrimination violations.

But Bhairavi Desai, a staff worker for the Taxi Workers' Alliance, which represents drivers, called the latest crackdown "pure scapegoating".

"It's just an attempt by a racist mayor to pit black people against brown and black workers of colour," he said. "It's a waste of resources to have black officers on corners hailing cabs."