The Washington Teachers’ Union and open-government advocates are urging the D.C. Council to slow down a vote that would curb access to information related to teacher evaluations, one of the most controversial aspects of the District’s education reform efforts.

A proposed amendment included in the Budget Support Act that the council is scheduled to vote on June 30 would block public-record requests for individual education evaluations, “effectiveness ratings,” observations and other assessments. Summary or aggregate data would still be available for public release.

District officials said that current laws protect personal information of teachers in D.C. Public Schools and that the measure is designed to protect charter school employees. Elizabeth Davis, president of the WTU, said the wording of the measure is confusing and potentially could have broad effects, including limiting the union’s ability to represent its members.

She called it a “secrecy provision” that the public should have more time to weigh in on.

“Without access to this data, there’s no way for the public or our union to tell whether the strategies DCPS uses — such as mayoral control — are helping students or simply creating school closures and high teacher turnover,” she wrote last week in a letter to Phil Mendelson (D), chairman of the D.C. Council.

Many states have recently passed or amended laws to protect teacher evaluations from being made public. Unions frequently advocate to keep such information private.

In 2010, the Los Angeles Times sparked a national debate when it published teachers’ names alongside “value-added” scores that attempt to measure a teacher’s effectiveness based largely on standardized tests. Many educators consider the scores misleading and their publication unfair.

District officials said individual DCPS records are exempt from public release because they are considered legally protected personnel files.

D.C. Council member David Grosso (I-At Large), chairman of the Education Committee, said the legislation in question seeks to extend that protection to public charter school employees.

New teacher evaluations are one of the most controversial aspects of reforms that were put in motion after then-Mayor Adrian Fenty (D) took control of the city’s public schools and appointed Michelle Rhee as chancellor. Hundreds of teachers lost their jobs after receiving low scores on their evaluations.

Given the high level of scrutiny of the system and the number of teachers who have lost their jobs, the union has been battling with the school system to release detailed information about teacher evaluations. The school system has declined to release data for individual teachers, even with names redacted, saying it would create an “unwarranted invasion of personal privacy.”

The union appealed the denial to Democratic Mayor Muriel E. Bowser’s office, which upheld the decision. Now, the union is suing.

Among the records requested, according to the union’s complaint in D.C. Superior Court, are those regarding terminations and evaluation scores for all teachers, including information such as school, grade, certification and subject — data that could potentially reveal teacher identities even if the names are redacted.

The proposed legislation addresses data requests from the Office of the State Superintendent of Education. Traditional and charter schools are required to provide information about teacher evaluations to the OSSE, which must report it to the federal government to comply with the provisions of the District’s waiver from the No Child Left Behind law. But, Grosso said, many charter school officials have been reluctant to provide data because they are afraid it could be made public.

The measure has passed as temporary emergency legislation twice since 2014 to encourage schools to comply with the law. This vote would make it permanent.

“We want to be very clear so that they can feel more at ease with submitting this data,” Grosso said in an e-mail.

Under the proposal, D.C. Public Schools or individual charter schools would still be able to release individual data if they choose to, he said.

Given the fact that the privacy measures have been on the books for more than a year, Grosso said he is frustrated that the union did not raise the issue until days before a vote was scheduled. The Budget Support Act was originally scheduled to be voted on Tuesday, but the vote was moved to June 30 to give the general counsel’s office more time to prepare it, he said.

Kevin M. Goldberg, president of the D.C. Open Government Coalition, said in a letter to Mendelson this month that the coalition is not necessarily opposed to the substance of the bill but that it has “fundamental objections” to the process. He said the Budget Support Act is “not a proper vehicle for denying D.C. residents access to public records.”

An exemption from public records warrants a more transparent process through its own bill or as part of a transparency-related measure, he said.

“We hope the Council will not rush to limit the public’s oversight of the school system, as there is still time to engage in the crucial thorough review of necessity of this exemption,” he said.

In a recent analysis of the progress of education reform in the District, the National Research Council found that the school system’s efforts to improve teacher quality are falling short in many schools. It noted that effective teachers are distributed unevenly across the city, with fewer highly rated teachers working in the highest-poverty schools.

It recommended that the city do a more careful analysis about how the evaluations are working and whether they are achieving their goals, and that it report more information related to teacher quality in traditional and charter schools.