CHICAGO – Mayor Rahm Emanuel said Thursday he's taking his offer of cash in exchange for a lengthier school day to Chicago's 108 charter schools, one week after a state labor board sought to block his longer-day campaign in district-run schools.

Emanuel is offering $75,000 in grant funding to schools and $800 to teachers who agree to lengthen their school day starting in January. He estimates the grants will cost Chicago Public Schools $5 million if all charter schools agree.

So far, he said 32 of 42 elementary charter schools have expressed interest in applying for the grants. Many charter schools already have a longer day than traditional schools, and only schools that don't already have that will be eligible for the grants.