A new clampdown on illegal taxi operators has been announced with a near trebling of the number of enforcement officers.

Under regulations that come into force today, drivers with three complaints will have to resit the knowledge test.

The exam has an 80% failure rate in some parts of the country.

Minister of State for Public Transport Alan Kelly said there will be 15 new enforcement officers appointed, almost trebling the number available to the National Transport Authority.

Last year the authority imposed 850 fines and carried out 50 prosecutions for more serious breaches of taxi regulations.

Some organisations representing taxi drivers have welcomed the new initiative, saying professional operators have nothing to fear.

There will also be a tightening up of rules governing foreign students applying for taxi licences and the rules will also make wheelchair access cabs more affordable.

"The new standards for wheelchair accessible vehicles will reduce the costs of purchasing wheelchair accessible taxis significantly and make more available for people with mobility impairments," said Mr Kelly.