Teachers in Colorado haven't gone on strike in 24 years, but on Monday, educators in Pueblo, will.

Schools in the D-60 will close on Monday and when they'll reopen is unclear. Teachers are demanding a retroactive cost of living raise and an increase in health insurance contributions.

The district offered staff a bonus and a "future" cost of living raise. The union turned that down.

Union president Suzanne Ethredge said there's more to the strike than money.

"We believe that we need to see the two percent and the additional money toward insurance," she told 9NEWS, "as well as have a truly open, honest discussion about respect and allowing our voices to be a part of the decision making in this district."

The district said they do not have the money to pay for a retroactive said. According to the district, a two percent increase in teacher pay would cost $1.2 million a year and it has received about $150 million less in state funding over the last eight years.

The last teacher strike in Colorado happened in Denver in 1994. It lasted five days.