By John Spina and Ben Chapman in Ny Daily News - The brigade of men and women who keep the city’s schools clean are calling on Mayor de Blasio to end a two-tier system which, they say, leaves thousands in their ranks underpaid. Under the system, about 800 of roughly 5,000 cleaners earn a base $23.85 an hour, while the rest, doing the same work get about five dollars less. A bureaucratic loophole is to blame, union reps and workers said in front of City Hall Wednesday. The lower paid workers were brought on by private contractors, while their higher paid counterparts were hired directly by the schools. None of the workers are city employees.