The leader of a group that champions the separation of church and state says a plan to permit a midday prayer break in some publicly funded New York City prekindergarten classes is "asking for a lawsuit."

The controversy comes as Mayor Bill de Blasio aims to expand his signature initiative to offer full-day pre-K classes for every 4-year-old. The plan depends in part on the participation of Jewish, Christian and Muslim schools.

Starting next September, pre-K classes will be permitted to break in the middle of the day for "non-program" activities such as prayer.

Additionally, schools will be invited to operate six days a week in order to meet the minimum number of classroom hours.

Civil liberties groups say the prayer break in a publicly funded classroom may violate the constitutional separation of church and state.