CHICAGO (CBS) – For more than 7,000 Chicago students there is no school again Wednesday as the first ever U.S. charter school strike continues.

Acero Schools teachers, joined by veterans of their Chicago Teachers Union, are on strike, demanding higher wages and smaller class sizes.

Acero Schools teachers on the picket line during first U.S. charter school strike.

“We are not going to quit until we get what’s right,” said Jesse Sharkey, CTU president.

“Right now we have 32 children in our classrooms. It’s not safe for our children,” said Caroline Rutherford, an Acero art teacher and union negotiator.

Charter teachers typically make about $9,000 less per year than teachers at a traditional public school, according to the National Alliance for Public Charter Schools. In Chicago the CTU says it’s even worse – an average of $13,000 less per year.

“We work longer days, we work a longer year, and we get paid significantly less,” Rutherford said.

Acero Schools CEO says they’ve made every effort to reach an agreement.

“We are very disappointed that union leaders have put their anti-charter political agenda ahead of the interests of our students,” said Acero CEO Richard Rodriguez. “There is absolutely no good reason to put students and parents through the upheaval of a strike.”

Union negotiator Andy Crooks said, “Rich Rodriguez is full of baloney. He doesn’t have a background in education. He’s in it for the money.”

But the teachers say they are putting charter schools on notice that they won’t take business as usual.

There are now about 7,000 charter schools in 43 states, but only 300 that are unionized.