The teachers' contract expires at the end of the month.
Under a new state law, 75 percent of all union members must vote for a strike. But next week's vote, set for June 6, does not mean Chicago teachers would automatically leave their classrooms.
At issue, teacher pay and a longer school day, as Mayor Rahm Emanuel wants.
"I can say assuredly, we are tired of being bullied, belittled, and betrayed by the district and by the City of Chicago," said Lewis. "Enough is enough."
CPS started receiving proposals from the union in January. The next month, both sides agreed to send the matter to a mediator, who will file his report July 16. Should both sides like it, the report would form the basis of a contract. But a rejection by either side sets in motion a 30-day no strike window -- meaning teachers could walk out of class as early as the end of August, right before school starts.
Before Friday, by the thousands they came, early last week, to back their union's opposition to proposals the Chicago Public Schools has talked about including in the next contract.
"Chicago school teachers are not going to accept the Board of Education's destructive proposals that are detrimental to the children of Chicago and to educators that dedicate their lives every day to teaching," said teacher Sarah Chambers.
Chicago teachers last walked the picket line in 1987. Their strike lasted 19 days. The union had a strike authorization vote during, but not before, negotiations.
"Our teachers have been demonized for the financial and economic crisis that they did not create," said parent Becky Malone. "They have been denied resources, counselors and programs that aid them in teaching our children particularly those that come from the most challenging circumstances."
CPS CEO Jean-Claude Brizard says he takes the strike authorization vote as a sign of disrespect for the entire process.
Brizard released a statement late Friday afternoon:
"Until negotiations with the independent fact finder are complete, and his compromise proposal has been released on July 16, any move toward a strike would only hurt our kids and school communities. Teachers deserve a raise for the great work they are doing, and they also deserve an opportunity to see the proposal being put on the table before asking them to authorize a strike."