Emanuel made the move without the cooperation of the library employees union, which has engaged in contentious negotiations with the mayor over the plan.
He will rehire 65 laid-off union workers and move 25 others from the downtown Harold Washington Library to the city's 76 branch libraries to keep the branches open on Monday afternoons.
"At some point, in every discussion, you have to know when that point is over and you're not going to get anywhere," Emanuel said of the talks with labor leaders.
Speaking at a library in the West Pullman neighborhood where he made the announcement, Emanuel said
"I said 'Look, if you're not going to do this,' they were notified I was going to take independent action," he said. "So they were clear about the partnership."
AFSCME Local 31 executive director Henry Bayer released a statement saying that rehiring some of the union library employees who the city had laid off "appears to be a step in the right direction, and a sign that the mayor is starting to appreciate the importance of libraries."
But Bayer also said Emanuel needs to go further to restore library hours. "Today's plan seems to leave branch libraries closed most Monday mornings and more than 100 library employees still out of work," Bayer said in the statement. "We urge the mayor to work with the union to finish the job for the people of Chicago, a world-class city that deserves libraries fully open and fully staffed."
Because the union workers being rehired are part-time employees, not librarians, Emanuel can change their work schedules without union agreement.
The changes will take effect Feb. 6.
Branch libraries had been scheduled to be open most Monday afternoons as part of the new city budget, but Emanuel shut them all day Monday when he couldn't reach agreement with the union. The branch libraries will remain closed Monday mornings.
Union leaders expressed concern about making library employees work six days a week.