The Chicago teachers' strike is putting US President Barack Obama's re-election campaign in a bind, pitting unions loyal to him against officials with ties to the White House.

The Obama camp needs to be careful not to upset the unions, which it needs for campaign funds and to do ground work leading up to the Nov 6 election, while not alienating independent voters who are worried about the Democrats being too close to powerful labor groups.

While not directly involved, Obama is associated in many minds with politics in his hometown, where one of his cabinet members, Education Secretary Arne Duncan, formerly oversaw the schools and now endorses the changes that have angered teachers.