UPDATED 10/14/11 8:36 a.m.

CHICAGO (CBS) — Chicago Public Schools officials say they have not received any response from the union for an invitation to a meeting on plans for a longer school day.

The union canceled a meeting that had been planned for this past Tuesday, and in a letter, schools chief executive officer Jean-Claude Brizard says he is looking forward to meeting with Chicago Teachers Union president Karen Lewis and her officers about the longer school day.

In the letter, Brizard asks Lewis to come and “discuss how we may be able to work in collaboration on adding another 25 schools with a longer day in January.

“I think it would be a great opportunity for us to meet at a school that is already implementing a longer school day so that we can see exactly how a school has integrated the 90 minutes of additional instructional time they have,” Brizard wrote.

Brizard says he is willing to come to the union offices, or host the meeting at CPS headquarters. But he says he has not heard back from the office.

Brizard sent three dates and times – on Wednesday, Thursday or Friday of next week – to hold the meeting.

While the union may not have responded to Brizard’s invitation, it did publish a news release Thursday slamming the push for a longer school day. The squabble is now set to go before a state labor panel.

In the release, the union claimed that the Illinois Educational Labor Relations Board had ruled that the school board’s actions interfere with employee rights, undermine the union and unlawfully discourage teachers from supporting the union’s leadership.

LISTEN: WBBM Newsradio’s Bob Roberts reports

But Chicago School Board spokeswoman Becky Carroll disagreed, saying the labor board has made no findings, and merely believes that the union’s complaint to the panel merits a hearing.

The union renewed its call on the school board to halt school-by-school votes on longer class schedules and to begin negotiations on the issue.

Carroll said the school board would not back down, would continue to ask teachers one school at a time to make the change, and would not roll back longer schedules at those schools that have already implemented them.

“We will continue to defend our position vigorously,” she said.

Union leadership has scheduled a 1 p.m. Friday news conference to discuss the labor board action.

In its release, the union said that the labor board has scheduled a Dec. 14 hearing on its complaint.

Brizard and Mayor Rahm Emanuel have devoted great attention toward lengthening the school day, and have asked the union to accept the change before the beginning of next school year.

The mayor also offered a 2 percent raise if the union agreed to the longer day.

But the union disagreed, complaining that the extra time teachers are being asked to work is not covered by a mere 2 percent raise. Thus, school officials asked individual schools to break ranks and agree to the longer school day on their own.

As a reward for lengthening their school days, each school was promised an extra $150,000 in funding from the Chicago Public Schools. Teachers at the schools are receiving $1,250 bonuses and the 2 percent raises.

Thirteen schools agreed to the offer.