A strike by Chicago's teachers entered a second week today frustrating the city's mayor, Rahm Emanuel, and posing unwelcome risks for President Barack Obama whose own relationship with the country's unions has come under increased scrutiny.
Hopes had risen at the end of last week that a draft deal heralded an end to the dispute and classrooms in the city's sprawling public school system - the largest in the United States - would be filled with students again this morning.
At the weekend, however, union leaders said they need more time to study it.
The stalling by the union led the Emanuel administration today to seek a court injunction to force the teachers to abandon the picket lines and return to work. The aggressive move was defended by Mr Emanuel. "This was a strike of choice and is now a delay of choice that is wrong for our children," he said.
While the new contracts offer pay rises they also seek to make it easier to replace underperforming teachers, for instance with a new evaluation system that would take greater account of how their pupils actually perform in exams.
The mayor is also resisting demands that teachers who have been laid off are given priority for new job openings; he wants those positions to be assigned simply on merit.
As his former Chief of Staff, Mr Emanuel is closely identified with Mr Obama. The White House has so far eschewed any direct involvement in the Chicago strike. But the President depends on union support for election funding and get-out-the-vote efforts. Anything that associates him with Mr Rahm's perceived assault on the teachers' union could be perilous.
"There's no doubt that this hurts President Obama," Michael Petrilli of, executive vice president of the Thomas B. Fordham told the New York Times. "He needs teachers to be energised and to go out and knock on doors and man phone banks for him. Right now they're watching his former chief of staff go toe to toe with the teachers' union in Chicago. This is not a position that the President wants to find himself in."
Many teachers in Chicago, a city that has seen a rash of street violence over the summer and where urban poverty is widespread, contend that it is wrong to evaluate teachers on the results of standardised tests because so many of their pupils come to school burdened by home difficulties that they cannot control.
The teachers' union said that because of a Jewish holiday it would return to consider the draft deal until today. "There's no trust for our members of the board," Chicago Teachers Union president Karen Lewis told reporters. "They're not happy with the agreement. They'd like it to actually be a lot better."
But some outside observers believe that the teachers would do well to accept what is on offer. "I'm hard-pressed to imagine how they could have done much better," said Robert Bruno, a professor or labour relations at the University of Illinois at Chicago. "This is a very impressive outcome for the teachers."