Updated 02/28/14 – 1:51 p.mm.

CHICAGO (CBS) — Chicago Public Schools CEO Barbara Byrd-Bennett has threatened to seek to remove the state certification of teachers who refuse to administer next week’s Illinois Standards Achievement Test, after many teachers planned a boycott.

WBBM Newsradio’s Bob Roberts reports the Chicago Teachers Union has issued an angry response.

CTU staff coordinator Jackson Potter said the union is appalled the district would threaten the certification of any teacher who refuses to administer the ISAT, or advises parents to opt-out their children.

“It’s pointless. It doesn’t make sense,” Potter said. “And yet, here the district is defending the defenseless. You can’t defend this.”

But Mayor Rahm Emanuel stood by Byrd-Bennett’s decision to threaten disciplinary action for teachers who refuse to give the test.

“The test is state-mandated. It will be out next year, so the teachers’ goal has been accomplished, but this year we’re going to continue it, because we have to,” Emanuel said. “The only people that can pull somebody out is not a teacher, but a parent, and that’s how it exists.”

Some parent groups have called for a boycott of the ISAT, and teachers at at least two schools have voted not to administer the test, saying students are forced to take too many standardized exams during the school year.

Teachers said the ISAT is no longer a factor in student promotion, graduation, or enrollment in selective-enrollment schools, so it makes no sense to force students to take it.

Next year, the ISAT will be replaced by two new standardized tests – one to determine promotion in grades three, six, and eight; the other for enrollment in selective-enrollment schools.

The planned boycott prompted Byrd-Bennett to send a letter to principals, saying she considers any teacher who encourages students not to take the ISAT, or advocates against the test on work time to be insubordinate.

CPS officials said the ISAT is required under the federal No Child Left Behind law.

Potter said Byrd-Bennett’s threat is absurd, but union lawyers were taking no chances.

“We’re disappointed. We think that they’re spreading misinformation. The Illinois State Board of Education has never – to our knowledge – revoked certification for a teacher for refusing to administer an exam, and yet the district’s making that claim. They’re scare tactics,” he said.

The mayor insisted Byrd-Bennett did the right thing.

“You can’t have a system that’s trying to achieve both educational advancement, and make sure we’re accountable and measuring it, where then … it’s up to everybody’s choice. So she made the right call,” Emanuel said.

Potter said teachers have a First Amendment right to express their opinion about the ISAT on their own time.

“When they’re off the clock, they can state their opinions. They can share information with the general public and parents about what their concerns are as it relates to whether or not instructional time is being wasted or misappropriated,” Potter said. “We’ll defend their right to do so.”

Potter said, if anything, the district’s stand is prompting more teachers and parents to want to join the boycott of the exam.