No sooner was the 39-year-long desegregation case against the Philadelphia School District officially closed yesterday than the threat of litigation by the teachers' union appeared on the horizon.

Commonwealth Court Judge Doris A. Smith-Ribner approved an agreement mandating extensive changes in the way many black and Latino students are educated in the city's public schools. The district and the Pennsylvania Human Relations Commission - original parties in the case filed in 1970 - signed off on the settlement last week.

However, the Philadelphia Federation of Teachers warned yesterday that the district leadership should not attempt to "evade their obligation to collectively bargain." The union's contract expires on Aug. 31; serious negotiations are expected to begin this week.

The court order means significant changes in where many teachers work, how they are chosen, and how much they earn, regardless of the terms of their contract.

The settlement is aimed primarily at the 85 "empowerment" schools; they are the lowest-performing in the district, and their student populations are often at least 90 percent minority.

At those schools, the settlement largely eliminates teacher seniority, raises salaries, and institutes new evaluations and professional development. It also channels extra resources to schools with a high proportion of inexperienced teachers, and calls for a weighted student funding formula based on the number of needy students.

Under the 2001 state takeover law, the School Reform Commission has the power to bypass negotiations and impose terms on the teachers' union, although it has never done so.

Jerry Jordan, PFT president, said the union might take legal action, but declined to be more specific.

In a letter to Smith-Ribner, Jordan suggested the district administration "is attempting to use the court and this litigation" to avoid negotiating.

Superintendent Arlene Ackerman has said she would prefer to negotiate the court-ordered teacher reforms, and plaintiffs' attorneys told the judge they would be bargained. But for the first time, SRC Chairman Robert Archie signaled he would be willing to circumvent the union.

"Maybe they didn't put children first," Archie said of previous commissions. But "we will use the power that the state has given us."

The desegregation lawsuit initially sought to force the district to bus students around the city for racial balance. But over the years, the suit became about equity for low-performing schools that were racially isolated, meaning that at least 90 percent of students were of one race.

When the suit was filed, 70 percent of schools were racially isolated. The district said it could not make current figures available. In 2004, according to an Inquirer analysis, about two-thirds of city schools still qualified for that designation.

Key to the settlement is Imagine 2014, Ackerman's five-year strategic plan. It stresses many of the same goals that Smith-Ribner has called for since taking over the case in 1993, including closing an achievement gap between black and minority students and white students, and reducing class sizes.

With Smith-Ribner's blessing, Ackerman now has a court order that says the district must implement her plan, estimated to cost $126 million in the 2009-10 school year.

Testifying before the judge yesterday, Ackerman said that when she took charge in June 2008, the district had "glaring racial disparities," with a high number of students of color in schools with poor facilities, low levels of parental involvement, a disproportionate number of inexperienced teachers, and a lack of rigor in curriculum.

"This settlement agreement is an opportunity for the adults in Philadelphia to do the right thing for all our children," she said. "Too many of our families have been waiting too long for things to change."

Ackerman has said she knows that some of the changes will not go over well with teachers, but that the changes could benefit them. Under her plan, teachers would make more money for teaching in tough schools, and getting stellar student results.

"I don't think we pay any of our teachers what they deserve," Ackerman said, adding that under her plan, "we'd have teachers making over $100,000. And in my estimation, they're worth it."

Smith-Ribner - at times a tough master who once threatened to jail former Superintendent David Hornbeck for disobeying court orders - seemed thrilled the long-fought case had finally ended.