It was put into effect last year for ATCs with some worrying results. All licensed staff that did the test was allowed to keep their license, even if they scored way below the required level. Students who failed had to wait three months before they could do the test again, and if they fail a second time they have to attend a language course.
If the atcs scored a lvl 4, they have to redo the test every 2 years, a lvl 5 you have to redo it after 5 years, and at lvl 6 you never have to do it again.
All atcs from native english speaking countries were excempted and given a lvl 6 without any testing.
Guess most airline pilots should not have too much of a problem passing this test, but will be interesting to see how our friends from Minhad, Al Dafra and Al Ain does....