Lewis was the president of the Chicago Teachers Union. She has been a member of the union since 1988. In 2010, Lewis, running with the Caucus of Rank and File Educators, gained control over the CTU by winning 60% of the vote in a run-off election. CORE ran an aggressive grassroots organizing campaign, and took a strong stance against school privatization. CORE accused the incumbent United Progressive Caucus of capitulating to corporate interests, silencing dissent within the union, and collaborating with the city to prevent union outreach at schools. CORE quickly took action to distinguish itself from UPC, the previous caucus controlling the CTU, reaffirm its grassroots support, and launch a campaign to defend public education. The new leadership cut pay for union officers and used the savings to expand outreach. CORE represented a major bloc of dissent at the 2012 AFT convention, and held signs in protest of Race to the Top during a speech from Vice President Joe Biden.
2012 Strike
In early September 2012 she led the Chicago Teachers Union on a 10-day strike. Emerging victorious, the union softened the proposed teacher evaluation system, prevented the instituting of merit pay, and ensured protections for veteran teachers in phased out schools. Prior to the strike she went through several months of negotiations with Chicago mayorRahm Emanuel and Emanuel appointee Chicago Public Schools board president Penny Pritzker. Lewis claimed that during a disagreement over lengthening the school day, Emanuel said, "Fuck you, Lewis."
Potential 2015 mayoral candidacy
In July 2014, Lewis set up an exploratory committee to consider running for mayor of Chicago in 2015. In a poll from the same month, Lewis bested Emanuel 45-36 in a hypothetical electoral contest. On October 13, 2014, her exploratory committee announced that she would not run, citing health issues.
Awards
2002 – National Board Certified Teacher in the area of Science for adolescents and young adulthood. 2015 – The Deborah W. Meier Hero in Education Award, presented by Fairtest. 2015 – The Mary E. Smith Foundation named a scholarship after Lewis: "The Karen Lewis CTU-CPS Excellence in Science Award."
Personal life
She is a convert to Judaism. An opera aficionado, she speaks French, Italian, and Latin, and plays flute and piano. On October 9, 2014, Lewis was hospitalized for a "serious illness". On October 13, a source confirmed that Lewis had been diagnosed with a cancerous brain tumor.