Ninety-four out of 97 Detroit Public Schools are closed Monday because instructors called in sick, school district spokeswoman Michelle A. Zdrodowski said. The so-called sickout came after teachers found out they would not be paid for two months of work.

Over the weekend, teachers learned they would not get salaries for May and June, according to Ivy Bailey, the interim president of the Detroit Federation of Teachers. Instructors were going to rally at 10 a.m. ET at the district’s central administration building.

“There’s a basic agreement in America: When you put in a day’s work, you’ll receive a day’s pay. DPS (Detroit Public Schools) is breaking that deal,” Bailey said. “Teachers want to be in the classroom giving children a chance to learn and reach their potential. Unfortunately, by refusing to guarantee that we will be paid for our work, DPS is effectively locking our members out of the classrooms.”

It’s unclear how many students Monday’s sickout affects, but about 46,000 students are enrolled in Detroit Public Schools, according to the Detroit Free Press.

The sickouts aren’t necessary, said district official Steven Rhodes.

Michigan Gov. Rick Snyder appointed Rhodes, a retired bankruptcy judge, in February to be the transition manager for Detroit Public Schools as state lawmakers work on improving academics and finances in the state’s largest school district, according to Snyder’s office.

The district has been in crisis for months. It has about $515 million in operating debt and is spending about $1,100 per student on debt service annually, the governor’s office has said.

On Sunday, Rhodes’ statement said, “It is unfortunate that the (teachers union) has chosen to make a statement in this way. I am on record as saying that I cannot in good conscience ask anyone to work without pay.

“Wages that are owed to teachers should be paid,” Rhodes said. “I understand the frustration and anger that our teachers feel. I am, however, confident that the Legislature will support the request that will guarantee that teachers will receive the pay that is owed to them. The (union’s) choice for a drastic call to action was not necessary.”

It’s not the first time Detroit public school teachers have protested by calling in sick en masse. In January, reacting to dilapidated and dangerously unsanitary conditions, teachers staged a sickout, forcing the closure of dozens of schools.

The problems included rat and roach infestations, black mold and pieces of ceiling falling.

Steve Conn, a local labor leader who organized that protest, told CNN that safety hazards, appalling building conditions, overcrowded classes and equipment shortages were serious concerns. “The conditions are terrible in the schools,” he said.