Dedham Public Schools teachers, school nurses and counselors have gone on strike after 21 months of contract negotiations.

In response to the Dedham Education Association's vote to strike Thursday afternoon, Dedham Public Schools Superintendent Michael Welch issued a statement canceling classes in all seven of the district’s schools on Friday Oct. 25.

The Dedham Education Association said they are fighting for better health insurance, fairer compensation, and language in the contract protecting staff from sexual harassment. Nearly all of its 270-plus members voted to strike.

“This is the second year that we've started the school year without a contract, and we're just not getting any movement on some of the key issues,” said Rachel Dudley, a high school social studies teacher and chairperson of the bargaining team for the Dedham Education Association. “The members have had enough.”

The Dedham Public Schools said in a statement that the vote to strike comes “just weeks before both sides are scheduled to meet with an independent arbitrator for a fact-finding session, in attempts to reach a fair and equitable contract.”

“As a district, we are saddened that our educators have chosen to consider this drastic and harmful action,” wrote Superintendent Welch. “We wholeheartedly appreciate and support our wonderful educators.”

Dudley said the Dedham Education Association has not met with the town administration since Aug. 1, and the decision to strike was carefully considered.

“It is always difficult when you know you're going to disrupt families’ lives, but the support we have gotten from the Dedham community has been overwhelmingly positive,” said Dudley, “We have been trying to get a deal for a very long time.”

Dudley said she and many of her colleagues will be picketing early Friday morning.

State law prohibits strikes by public employees, making the strike illegal. In a statement, the Dedham Public Schools wrote they filed a petition with the Massachusetts Department of Labor Relations in the hopes they will intervene.

Dudley said the Dedham Education Association is anticipating a fine from the state agency.