UPDATED 01/06/12 6:33 a.m.

CHICAGO (CBS) — When Mayor Rahm Emanuel’s budget passed, the plan called for Chicago public libraries to close only on Monday and Friday mornings.

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But as WBBM Newsradio’s Bob Conway reports, that has now changed. The libraries will now close all day on Mondays, and aldermen who say they had an agreement with the mayor are stunned and infuriated.

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“That’s not what was proposed or voted on. It’s completely contrary. We need to sit down quickly and get back to the original agreement, which was keep those libraries open” every day, said Ald. Scott Waguespack (32nd), who led the charge against the library cuts.

The mayor’s plan to reduce library hours and impose draconian job cuts that would impact library services at all hours fast emerged as the most controversial element of the mayor’s 2012 budget.

Aldermen from across the city decried the mayor’s decision to reduce corporate fund support for libraries by $10 million — even as the city continues to build new libraries on top of the 59 constructed under former Mayor Richard M. Daley.

Librarians delivered petitions bearing 4,000 signatures and staged a “read-in” outside the mayor’s office.

Twenty-eight aldermen signed a budget protest letter to the mayor demanding that the cuts be reversed.

To soften the blow — and pave the way for unanimous approval of his first budget — Emanuel agreed to restore $3.3 million cut from Chicago Public Libraries.

Instead of laying off 284 library employees, he vowed to fire just 184. And although he stood firm on his original plan to close the libraries on Monday and Friday mornings, the mayor agreed that those closings would not apply during the 19 weeks when school is out.

Now, that plan is apparently out the window.

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The Chicago Public Library announced on its Facebook page that “branch locations will now be open Tuesday-through-Saturday and close on Mondays.”

Deputy mayoral press secretary Jennifer Hoyle explained the change in an e-mail to the Chicago Sun-Times.

“Closing for two half-days, rather than one full day was contingent upon the union agreement to give us increased flexibility in scheduling,” Hoyle wrote.

“We are talking to the unions, but haven’t yet reached an agreement. For that reason, in the meantime, the branch libraries will be closed on Monday.”

Anders Lindall, a spokesman for AFSCME Council 31 representing the 176 library employees, acknowledged that the union is negotiating with the city. But, he categorically denied that the union had forced the city’s hand.

“Whether a reduction in hours comes for four hours on two days a week or eight hours on one day is not acceptable to people of the city who want and deserve access to their libraries at all times. They shouldn’t be forced to accept reduced access,” Lindall said.

“We haven’t seen a proposal from the city that would prevent those reduced hours. We’ve had discussions. Those discussions continue. We hope to reach an agreement to prevent reduced hours and rescind the layoffs.”

Waguespack doesn’t care who is to blame. He’s livid that the compromise aldermen thought they had reached with Emanuel has been reversed in a way that could devastate some of his constituents.

“Monday is the day they want to get out of the house looking for work on the computer. It’s the day they want to get the kids out of the house and into the reading room,” Waguespack said. “It would be detrimental to people who have relied on kicking off the week. Especially in the winter, you get out of the house and head straight for the library.”

Even Ald. Pat O’Connor (40th), the mayor’s City Council floor leader, was taken aback by the all-day Monday closing.

“We budgeted for two half-days,” O’Connor said. But, he added, “It would require the unions to agree to it.”

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The Sun-Times Media Wire contributed to this report.