Even taxis that are legal are still likely to carry passengers without documenting them, according to Anton Zaboronov, a frequent traveller in unlicensed cabs.

The embassy highly discourages taking private unlicensed cabs in lieu of licensed taxicabs while in Kazakhstan.

While most jurisdictions require taxicab operators to be licensed, many unlicensed cabs are in operation.

By acting as a barrier to entry to the taxi market, it has the unintended consequence of creating a market for unlicensed cabs, especially in areas that tend to be underserved by medallion cabs.

In America, there is significant anecdotal evidence that unlicensed cabs are mostly found in working-class neighborhoods of large cities.

Moreover, residents of such neighborhoods may favor unlicensed cabs even if licensed taxis are available.

The U.S. Embassy advises its employees to avoid the use of unlicensed cabs and recommends using only radio dispatched taxis.

Last year, the city Taxi and Limousine Commission, under Mr. Lynn, who was then the chairman, stepped up its enforcement against unlicensed livery cabs.

Its proposals include the elimination of the free market in tax medallions, the creation of a new medallion for car services in the outer boroughs and a six-fold increase in enforcement against unlicensed cabs.

(The only way to spot the difference is to check for a meter: unlicensed cabs don't have them.)