In the recent Chicago Public Schools contract offer, which now lingers in a sort of political purgatory, teachers were offered a pay raise, but there was a big catch: CPS educators would essentially be paying for the salary increase by sacrificing the most experienced members of their teaching force.

An early-retirement buyout program was the linchpin of the Board of Education’s since-rejected offer – and it’s one of the main reasons why Chicago Teachers Union representatives voted down the deal, according to union officials.

The board was offering $1,500 per year of service to teachers of retirement age and $750 to support staff to leave, according to the CTU. If at least 1,500 teachers and 700 other staffers took advantage of the buyout offer, the contract would stand, according to the CPS offer.

But, if not enough employees signed up for early retirement, then CPS could reopen the contract – which union members feared would lead to layoffs.

With that prospect looming and, among other things, the concern of a brain drain as experienced educators walked out the door, the CTU’s bargaining team of 40 union representatives voted down the deal unanimously on Monday.

At a press conference on Tuesday, CTU President Karen Lewis said the union voted down the contract offer because, “No. 1 it would have pushed out 2,200 of our seasoned, experienced educators, disproportionately impacting African-American and Latino educators. It will lead to ballooning class sizes and the cuts the board proposed were solely out of our pockets.”

Related Article: Declining Numbers Of Black Teachers At CPS

Fifty-four percent of teachers with more than 20 years experience are black or Latino, whereas only 22 percent of new teachers are, according to a Better Government Association analysis of 2012 state data. New teachers make about $48,000 a year, while those with 20 years or more experience make an average of $88,000.

(For past BGA coverage on race among CPS educators, click here and here.)

A CTU official said that CPS officials told the union that the buyouts would initially cost CPS, but ultimately could save the system as much as $70 million in each of the third and fourth years of the four-year contract. CPS did not answer questions about potential cost savings, or anything else for this story.

At the same time, teachers and support staff who didn’t take buyouts were being promised raises – there were no raises proposed for the first year of the deal, 2.75 percent pay hikes planned in the second year, 3 percent in the third and 1 percent in the fourth – that would cost the district between $50 million and $70 million a year.

In the deal offered by CPS, the district promised no economic layoffs, but did not explicitly promise to replace all staff who take buyouts.

The CTU fears CPS would dedicate less funding per child, which could translate into open teaching positions not being filled.

Jim Cavallero, a special education teacher at Chicago Academy High School, said another major concern is that undue pressure would be put on veteran teachers. A majority of these teachers work in schools on the South and West sides and it would be problematic if these schools – many with poor students – were left with mostly new and inexperienced teachers.

“Schools need a balance of experienced teachers and new ones,” he said at a press conference where members of the CTU’s bargaining team discussed why they voted against the board’s proposal. “We cannot allow these teachers to be pushed out when they are needed most.”

About 5,500 CPS teachers have more then 20 years experience, according to state data. Because retirement eligibility is a combination of years of service and age, the union indicated fewer than 3,000 would be eligible for early retirement.

Robert Bruno, professor of labor education at the University of Illinois, said that taking a deal that would allow the district to crack back open the contract would be a huge risk for the union.

“I can see the teachers saying, ‘We have real skin in the game but what CPS is offering us isn’t really solid,’” he said.

CTU Vice President Jesse Sharkey said that, on the surface, the idea of an early-retirement buyout could be a win-win. Those who are on the verge of leaving get some cash while the school district gets some fairly quick potential savings.

But many CTU members were nervous about how the contract would play out, and felt that Mayor Rahm Emanuel’s administration ultimately could not be trusted, Sharkey said.