JERSEY CITY, N.J. — Teachers in Jersey City voted to strike Friday for the first time in 20 years after contract negotiations fell through.

Thousands of union members were out of the classroom and on the picket lines outside Jersey City schools after no decision was reached on a new contract for the teachers’ union during the school board meeting. The last time Jersey City teachers went on strike was 20 years ago and lasted five days.

The union had been in contract talks with the city for months. The sticking point for them seems to be healthcare.

Mayor Steven Fulop called the strike "unfortunate + avoidable" on Twitter, saying he believed the Board of Education offered the union a 3.5 percent increase in the first year, and 2.7 percent increase the second year.

"I don’t have more info but this seemed very fair," the mayor tweeted.

President of the Jersey City Education Association, Ron Greco, said teachers have been asked to stop picketing for the day between 10 and 11 a.m. after the district reached out to union officials about resuming discussions.

However, teachers outside Frank R Conwell No. 3 said "we're not dispersing until school is over."

Greco's update came shortly after he told PIX11 that he "challenged the school district to meet me this morning. I am ready, willing and able to finish this."

Regardless of the outcome, Greco said there was no chance of averting a strike before school starts Friday morning.

Parents should have received an automated message informing them that their child’s teacher would walk off the job Friday.

According to the Jersey City Public Schools website, schools will be open with a half-day schedule as both sides continue negotiating over the weekend.

Morning and after-school programs are suspended, but breakfast and lunch still will be provided for students.

Superintendent Dr. Marcia V. Lyles vowed to continue to work to come to an agreement without affecting the children.

“We will need to make provisions to ensure the safety of your children. That will be our paramount concern. I also want you to know that our negotiating team has been working tirelessly to find ways to address teacher concerns while ensuring that we can maintain the quality of our programs," Lyles said.

At least 400 substitute teachers were called to replace striking teachers Friday, a substitute attempting to pass the picket line at Frank R Conwell No. 3 told PIX11.

#BREAKING Jersey City teachers on strike blocked substitute teacher from getting into the Frank Conwell school; sub called 911. @PIX11News pic.twitter.com/D1NhNXhYjY — Anthony DiLorenzo (@ADiLorenzoTV) March 16, 2018

Cameras captured tense moments as striking teachers blocked substitutes from entering the school.

"We’re not going to respect you, and now we’re going to remember you. You’re never going to be in our union now," one teacher said to a substitute as the two clashed in the street.

The substitute responded, saying she is already part of the union.

This prompted the teacher to reply, "then you would be on the line, wouldn't you? Make up your mind."

“We’re not going to respect you!” Picketing teacher chastises substitute who tried but failed to cross the picket line as tensions run high amid school strike in Jersey City. @PIX11News pic.twitter.com/LMWSPmm0K6 — Anthony DiLorenzo (@ADiLorenzoTV) March 16, 2018

Substitutes eventually made it inside the school with police escort.

Among the protestors Friday were a mother and her daughter, a student, holding up signs in solidarity with the teachers.

"We felt that it’s important to support the most important people in our lives, which are educators, our teachers, and it just doesn’t feel right to go against that," mother Elsa Vazquez said. "We want to support their efforts."

When asked what she hoped missing school to protest would teach her daughter, Vazquez replied, "to stand up for what is right, what is just. To be strong and to fight for rights. Not just for yourself, but for others, too."

Other parents said on social media they also plan to keep their children home from school.