The Chicago Teachers Union narrowly voted Wednesday evening to approve a safety agreement between the union and the district supporting in-person classes. 

The agreement came as children returned to classes on Wednesday in the nation’s third-largest school district following five days of canceled classes as a result of a standoff with the teachers union on coronavirus protocols.

Chicago Mayor Lori Lightfoot gets a COVID-19 booster vaccine at Michele Clark High School on Nov. 12, 2021 (Photo by Scott Olson/Getty Images)

CHICAGO MAYOR LORI LIGHTFOOT TESTS POSITIVE FOR COVID-19

The safety plan approved by the union includes expanded testing and metrics to shut down individual schools during outbreaks if the outbreak infects 25% of staff.

Leaders of the union gave their tentative approval two days earlier allowing children to return. They urged members to accept it, acknowledging that teachers didn’t get initial demands, including a commitment to use remote learning district-wide during a surge of COVID-19 infections.

Union President Jesse Sharkey said the agreement "wasn’t a home run" but was "as much as we could get right now."

Students at the Mt. Greenwood Elementary School in Chicago depart after a full day of classes Monday, Jan. 10, 2022. (AP Photo/Charles Rex Arbogast)

The vote passed with 55% approval, according to the Chicago Sun-Times.

CHICAGO MAYOR LIGHTFOOT SLAMS TEACHERS' UNION FOR 'ILLEGAL WALK-OUT,' REJECTS PROPOSAL FOR REMOTE LEARNING

Chicago Mayor Lori Lightfoot, a Democrat, reacted to the news on Twitter. 

"We are pleased we have come to an agreement w/@CTULocal1 that guarantees predictability and stability for the rest of the school year," Lightfoot posted. "We all agree we must prioritize the health and well-being of everyone in our school communities including our kids, families and staff. "

Lightfoot had previously labeled the teacher walkout "illegal."

The Chicago skyline, photographed from outside the Adler Planetarium in Chicago, Illinois (Raymond Boyd/Getty Images)

"To be clear, what the Chicago Teacher’s Union did was an illegal walk-out," Lightfoot said over the weekend. "They abandoned their posts and they abandoned kids and their families."

Associated Press contributed to this report