The union said the unanimous vote Wednesday came after reports indicated Martinez was evaluating the closure of more than 100 schools and other measures to balance the CPS budget.
The CTU and CPS are in contract talks right now.
"CEO Martinez spent last week boasting about the district's new five-year plan, much of which he essentially copied from our union's contract proposals," CTU President Stacy Davis Gates said in a statement. "At the same time he's heralding this as his historic vision, he's telling our members at the bargaining table there's no money to implement transformation for our schools."
On Friday, multiple sources told ABC7 Chicago that Mayor Brandon Johnson asked Martinez to resign the previous day.
In a letter to families, CPS said Martinez is focused on building on the positive momentum of the new school year.
Martinez, himself a CPS graduate, was hired by former Chicago Mayor Lori Lightfoot. His relationship with Mayor Johnson reportedly became strained after he refused to take out a short-term high-interest loan to help pay for a new teachers contract, which is still in contentious talks.
"Only 20% of our schools have libraries and librarians. He's got to have a better idea of how to envision our school district than just cutting it and consolidating it," Davis Gates said.
Sources say CPS conducted an analysis, but has no plans to close schools.
"If you look at what's going on over the last several weeks, it is a build up of a smear campaign, who is standing between CTU and the taxpayers in terms of negations," 32nd Ward Ald. Scott Waguespack said.
As the CPS CEO tries to tune out the outside noise, the challenges he faces include paying for a new teachers contract and an expected $500 million budget deficit next school year.
Over 400 principals and assistant principals signed a letter of support for Martinez. Twenty aldermen also did the same.
Waguespack is one of 20 alders who signed a letter of support for Martinez. They accuse the CTU and the mayor's office of orchestrating a smear campaign against Martinez because of the costly loan that Waguespack says will cost the taxpayers double.
Davis Gates said replacing Martinez is about smaller classroom sizes, more librarians and saving the jobs of teachers, clinicians and paraprofessionals.
"I find it reprehensible that she would step into this realm and act like somehow what she's trying to do is for the good of the students and for the families of the city," Waguespack said.
Martinez is reportedly feeling out the school board. The mayoral-appointed board must green light his ouster if Martinez does not voluntarily resign.
"The question should be: Why is Pedro out of step with his Board of Education, with his mayor who has hired him?" Davis Gates said. "Remember, he was the chief financial officer of the Chicago Public Schools, and he has a history of putting these loans through the Board of Education. So the hypocrisy is at an all-time high."
The board of education's next public meeting is Thursday. ABC7 Chicago has left a message for the school board president, but it was not returned.
It is not known yet if Martinez's future is on the agenda.
For now, Martinez is not voluntarily resigning.