The massive teacher strike in Chicago offers a high-profile test for the nation's teacher unions, which have seen their political influence threatened as a growing reform movement seeks to expand charter schools, get private companies involved with failing schools and link teacher evaluations to student test scores.
Union leaders are taking a major stand on teacher evaluations, one of the key issues in the Chicago dispute. If they lose there, it could have ripple effects around the country.
The American Federation of Teachers (AFT) and the National Education Association, the nation's two largest teacher unions, have been playing defence in jurisdictions around the country as Republicans and Democrats alike seek greater concessions in a bid to improve ailing public schools.
After decades of growth in membership and influence, the unions now are in a weaker position, said Rick Hess of the American Enterprise Institute, a non-partisan think tank.
"They are playing on more hostile terrain and they are facing opponents the likes of which they have not had to face before," Hess said.
The strike also has implications for the presidential race because it pits the Chicago Teachers Union, the AFT's oldest local, against Chicago Mayor Rahm Emanuel, former chief of staff to President Barack Obama. Obama is counting on the strong support of unions to help his re-election campaign, but his administration has sided with some of the reforms unions are railing against.
Teachers walked off the job Monday for the first time in 25 years over issues that include pay raises, classroom conditions, job security and teacher evaluations. Emanuel is trying to extract more concessions from teachers while the school district faces a nearly $700 million deficit.