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 and the National Education Association -- the nation's two largest teacher unions -- have been playing defense 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 nonpartisan 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.
Major teacher strikes have been rare in recent years, compared with the 1960s and 1970s, when teachers went on strike frequently for better pay and improved bargaining rights. While unions generally got what they wanted in the past, they face a tougher climate today.
With the weak economy, unions have seen massive teacher layoffs, increased class sizes and school districts unable or unwilling to boost teacher salaries. Like other public employee unions, they are also under attack from Republican governors like Scott Walker of Wisconsin, who signed a measure last year to curb collective bargaining rights and limit benefits for state workers.
The 2.2-million member NEA has lost more than 100,000 members since 2010, as fewer public school teachers are hired and more charter schools open, most of which are not unionized. At the 1.5 million-member AFT, years of steady growth have leveled off.
"They certainly are on the defensive," said Richard Ingersoll, a professor of education and sociology at the University of Pennsylvania. "They are under attack. A lot of times they are demonized. On the other hand there's really smart and progressive elements in the teacher's movement who want to get out ahead of this and do it in a way that's fair."
In the past, teachers unions could count on a Democratic White House to fight back on their behalf. But Obama's education secretary, Arne Duncan, is a former head of Chicago Public Schools who has pushed for many of the changes that unions oppose.
"In many ways the Obama administration has signed onto the very conservative set of reforms that the education community is imposing on teachers," said Richard Kahlenberg of the Century Foundation, a nonpartisan think tank in Washington.
Both the NEA and the AFT have strongly endorsed Obama's re-election despite his administration's support of policies to expand charter schools, weaken tenure and base teacher evaluations on how much student performance improves. The Chicago strike could test that alliance, as Obama declines to take a public stand supporting the union.
Evaluating teachers on how much their students improve is a key component of Obama's education policy. His administration has approved waivers freeing many states from the most onerous requirements of the Bush-era No Child Left Behind law. In order to get a waiver, each state had to promise to show in other ways that its students and schools are improving, and to more closely link teacher evaluations to student test scores.
The Chicago union argues that the new teacher evaluation system relies too heavily on standardized test scores without considering outside factors such as student poverty, violence and homelessness that can affect performance.
Hess said the Chicago strike has become an important test case after unions lost their effort to recall Wisconsin's governor.
"If it looks like the union folds, especially on the heels of Wisconsin, it's a huge blow for the unions," Hess said. "If the union seems to win, that's going to be a blow to reform-minded mayors and puts some wind into the sails of unions."
There are major differences, though, between the cases in Wisconsin and Chicago.
While Walker effectively challenged public employee unions' collective bargaining rights, both sides in Chicago have been negotiating over traditional labor-management issues. The district proposed a 16 percent raise over four years and the two sides have essentially agreed on a longer school day. But job security and a new teacher evaluation system remained in dispute.
AFT President Randi Weingarten said the union didn't want to strike, but did so only as a last resort after negotiations "that left CTU members feeling disrespected." Among the issues she cited was the mayor's decision this year to strip teachers of an agreed-upon 4 percent raise.
"This is a long-term battle that everyone's going to watch," said Eric Hanuskek, a senior fellow in education at the Hoover Institution of Stanford University. "Other teachers unions in the United States are wondering if they should follow suit."
Teacher unions also are growing nervous about how they are portrayed in an upcoming Hollywood movie called "Won't Back Down," set to open in theaters on Sept. 28. The film tells the story of a mother's quest to take control of her daughter's failing elementary school.
Weingarten has blasted the movie as "using the most blatant stereotypes and caricatures I have ever seen" and unfairly blaming unions for the nation's school woes. Union leaders were even more outraged that the movie was screened at the Democratic National Convention in Charlotte, N.C., and that Los Angeles Mayor Antonio Villaraigosa -- the convention chairman -- attended the screening.